diff --git a/backend/models.py b/backend/models.py
index c459c1b..bdc93a8 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -13,6 +13,7 @@ class User(Base):
 
     id = Column(Integer, primary_key=True, index=True)
     username = Column(String(50), unique=True, nullable=False, index=True)
+    display_name = Column(String(64), nullable=False)
     password_hash = Column(String(200), nullable=False)
     profile_picture = Column(String(255), nullable=True)
     bio = Column(Text, nullable=True)
@@ -149,6 +150,7 @@ class LoginRequest(BaseModel):
 
 class RegisterRequest(BaseModel):
     username: str
+    display_name: str
     password: str
     confirm_password: str
 
@@ -178,6 +180,7 @@ class PushSubscriptionRequest(BaseModel):
 class UserProfileResponse(BaseModel):
     id: int
     username: str
+    display_name: str
     profile_picture: str | None
     bio: str | None
     online: bool
diff --git a/backend/routes/account.py b/backend/routes/account.py
index 0448417..3b23b6f 100644
--- a/backend/routes/account.py
+++ b/backend/routes/account.py
@@ -6,7 +6,7 @@ from constants import OWNER_USERNAME
 from dependencies import get_current_user, get_db
 from models import LoginRequest, RegisterRequest, User, CryptoPublicKey, CryptoBackup
 from utils import create_token, get_password_hash, verify_password
-from validation import is_valid_password, is_valid_username
+from validation import is_valid_password, is_valid_username, is_valid_display_name
 
 router = APIRouter()
 
@@ -17,6 +17,7 @@ def convert_user(user: User) -> dict:
         "last_seen": user.last_seen.isoformat(),
         "online": user.online,
         "username": user.username,
+        "display_name": user.display_name,
         "profile_picture": user.profile_picture,
         "bio": user.bio,
         "admin": user.username == OWNER_USERNAME
@@ -58,6 +59,7 @@ def login(request: LoginRequest, db: Session = Depends(get_db)):
 @router.post("/register")
 def register(request: RegisterRequest, db: Session = Depends(get_db)):
     username = request.username.strip()
+    display_name = request.display_name.strip()
     password = request.password.strip()
     confirm_password = request.confirm_password.strip()
 
@@ -75,7 +77,13 @@ def register(request: RegisterRequest, db: Session = Depends(get_db)):
     if not is_valid_username(username):
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
-            detail="Имя пользователя должно быть от 3 до 20 символов и не содержать пробелов"
+            detail="Имя пользователя должно быть от 3 до 20 символов и содержать только английские буквы, цифры, дефисы и подчеркивания"
+        )
+
+    if not is_valid_display_name(display_name):
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Отображаемое имя должно быть от 1 до 64 символов и не может быть пустым"
         )
 
     if not is_valid_password(password):
@@ -107,6 +115,7 @@ def register(request: RegisterRequest, db: Session = Depends(get_db)):
     hashed_password = get_password_hash(password)
     new_user = User(
         username=username,
+        display_name=display_name,
         password_hash=hashed_password,
         online=True,
         last_seen=datetime.now()
diff --git a/backend/routes/messaging.py b/backend/routes/messaging.py
index 6c1f2f2..54cc0e7 100644
--- a/backend/routes/messaging.py
+++ b/backend/routes/messaging.py
@@ -48,16 +48,17 @@ def convert_message(msg: Message) -> dict:
             reactions_dict[emoji]["count"] += 1
             reactions_dict[emoji]["users"].append({
                 "id": reaction.user_id,
-                "username": reaction.user.username
+                "username": reaction.user.display_name
             })
 
     return {
         "id": msg.id,
+        "user_id": msg.author.id,
         "content": msg.content,
         "timestamp": msg.timestamp.isoformat(),
         "is_read": msg.is_read,
         "is_edited": msg.is_edited,
-        "username": msg.author.username,
+        "username": msg.author.display_name,
         "profile_picture": msg.author.profile_picture,
         "reply_to": convert_message(msg.reply_to) if msg.reply_to else None,
         "reactions": list(reactions_dict.values()),
@@ -88,7 +89,7 @@ def convert_dm_envelope(envelope: DMEnvelope) -> dict:
             reactions_dict[emoji]["count"] += 1
             reactions_dict[emoji]["users"].append({
                 "id": reaction.user_id,
-                "username": reaction.user.username
+                "username": reaction.user.display_name
             })
 
     return {
diff --git a/backend/routes/profile.py b/backend/routes/profile.py
index 8eb6563..6b0d800 100644
--- a/backend/routes/profile.py
+++ b/backend/routes/profile.py
@@ -11,12 +11,14 @@ import io
 from dependencies import get_db, get_current_user
 from models import User, UpdateBioRequest, UserProfileResponse
 from pydantic import BaseModel
+from validation import is_valid_username, is_valid_display_name
 
 router = APIRouter()
 
 # Request models
 class UpdateProfileRequest(BaseModel):
-    nickname: str | None = None
+    username: str | None = None
+    display_name: str | None = None
     description: str | None = None
 
 # Create uploads directory if it doesn't exist
@@ -102,6 +104,7 @@ async def get_user_profile(
     return {
         "id": current_user.id,
         "username": current_user.username,
+        "display_name": current_user.display_name,
         "profile_picture": current_user.profile_picture,
         "bio": current_user.bio,
         "online": current_user.online,
@@ -121,19 +124,32 @@ async def update_user_profile(
     updated = False
     
     # Update username if provided
-    if request.nickname is not None:
-        nickname = request.nickname.strip()
-        if len(nickname) < 3:
-            raise HTTPException(status_code=400, detail="Username must be at least 3 characters long")
-        if len(nickname) > 50:
-            raise HTTPException(status_code=400, detail="Username must be 50 characters or less")
+    if request.username is not None:
+        username = request.username.strip()
+        if not is_valid_username(username):
+            raise HTTPException(
+                status_code=400, 
+                detail="Имя пользователя должно быть от 3 до 20 символов и содержать только английские буквы, цифры, дефисы и подчеркивания"
+            )
         
         # Check if username is already taken by another user
-        existing_user = db.query(User).filter(User.username == nickname, User.id != current_user.id).first()
+        existing_user = db.query(User).filter(User.username == username, User.id != current_user.id).first()
         if existing_user:
-            raise HTTPException(status_code=400, detail="Username already taken")
+            raise HTTPException(status_code=400, detail="Это имя пользователя уже занято")
         
-        current_user.username = nickname
+        current_user.username = username
+        updated = True
+    
+    # Update display name if provided
+    if request.display_name is not None:
+        display_name = request.display_name.strip()
+        if not is_valid_display_name(display_name):
+            raise HTTPException(
+                status_code=400, 
+                detail="Отображаемое имя должно быть от 1 до 64 символов и не может быть пустым"
+            )
+        
+        current_user.display_name = display_name
         updated = True
     
     # Update bio if provided
@@ -150,12 +166,14 @@ async def update_user_profile(
         return {
             "message": "Profile updated successfully",
             "username": current_user.username,
+            "display_name": current_user.display_name,
             "bio": current_user.bio
         }
     else:
         return {
             "message": "No changes made",
             "username": current_user.username,
+            "display_name": current_user.display_name,
             "bio": current_user.bio
         }
 
@@ -197,6 +215,31 @@ async def get_user_by_username(
     return UserProfileResponse(
         id=user.id,
         username=user.username,
+        display_name=user.display_name,
+        profile_picture=user.profile_picture,
+        bio=user.bio,
+        online=user.online,
+        last_seen=user.last_seen,
+        created_at=user.created_at
+    )
+
+@router.get("/user/id/{user_id}")
+async def get_user_by_id(
+    user_id: int,
+    db: Session = Depends(get_db)
+):
+    """
+    Get user profile by user ID
+    """
+    user = db.query(User).filter(User.id == user_id).first()
+    
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+    
+    return UserProfileResponse(
+        id=user.id,
+        username=user.username,
+        display_name=user.display_name,
         profile_picture=user.profile_picture,
         bio=user.bio,
         online=user.online,
diff --git a/backend/validation.py b/backend/validation.py
index d145b6f..376fdc2 100644
--- a/backend/validation.py
+++ b/backend/validation.py
@@ -3,7 +3,17 @@ import re
 def is_valid_username(username: str) -> bool:
     if len(username) < 3 or len(username) > 20:
         return False
-    if re.search(r'[\s\u180E\u200B-\u200D\u2060\uFEFF]', username):
+    # Only allow English letters, numbers, dashes and underscores
+    if not re.match(r'^[a-zA-Z0-9_-]+$', username):
+        return False
+    return True
+
+
+def is_valid_display_name(display_name: str) -> bool:
+    if len(display_name) < 1 or len(display_name) > 64:
+        return False
+    # Check if not blank (only whitespace)
+    if not display_name.strip():
         return False
     return True
 
diff --git a/frontend/src/core/api/profileApi.ts b/frontend/src/core/api/profileApi.ts
index 53c0962..98ca83e 100644
--- a/frontend/src/core/api/profileApi.ts
+++ b/frontend/src/core/api/profileApi.ts
@@ -4,7 +4,8 @@ import type { UserProfile } from "@/core/types";
 
 export interface ProfileData {
     profile_picture?: string;
-    nickname?: string;
+    username?: string;
+    display_name?: string;
     description?: string;
 }
 
@@ -26,7 +27,8 @@ export async function loadProfile(token: string): Promise<ProfileData | null> {
             // Map backend fields to frontend fields
             return {
                 profile_picture: data.profile_picture,
-                nickname: data.username,
+                username: data.username,
+                display_name: data.display_name,
                 description: data.bio
             };
         }
@@ -69,7 +71,8 @@ export async function updateProfile(token: string, data: Partial<ProfileData>):
     try {
         // Map frontend fields to backend fields
         const backendData = {
-            nickname: data.nickname,
+            username: data.username,
+            display_name: data.display_name,
             description: data.description
         };
 
@@ -126,3 +129,23 @@ export async function fetchUserProfile(token: string, username: string): Promise
         return null;
     }
 }
+
+/**
+ * Fetches user profile data by user ID
+ */
+export async function fetchUserProfileById(token: string, userId: number): Promise<UserProfile | null> {
+    try {
+        const response = await fetch(`${API_BASE_URL}/user/id/${userId}`, {
+            headers: getAuthHeaders(token)
+        });
+
+        if (response.ok) {
+            return await response.json();
+        }
+
+        return null;
+    } catch (error) {
+        console.error('Error fetching user profile by ID:', error);
+        return null;
+    }
+}
diff --git a/frontend/src/core/types.d.ts b/frontend/src/core/types.d.ts
index 0c13a15..47fc9d6 100644
--- a/frontend/src/core/types.d.ts
+++ b/frontend/src/core/types.d.ts
@@ -62,6 +62,7 @@ export interface Reaction {
 
 export interface Message {
     id: number;
+    user_id: number;
     username: string;
     content: string;
     is_read: boolean;
@@ -111,6 +112,7 @@ export interface User {
     last_seen: string;
     online: boolean;
     username: string;
+    display_name: string;
     admin?: boolean;
     bio?: string;
     profile_picture: string;
@@ -130,6 +132,7 @@ export interface User {
 export interface UserProfile {
     id: number;
     username: string;
+    display_name: string;
     profile_picture?: string;
     bio?: string;
     online: boolean;
@@ -163,6 +166,7 @@ export interface LoginRequest {
  */
 export interface RegisterRequest {
     username: string;
+    display_name: string;
     password: string;
     confirm_password: string;
 }
diff --git a/frontend/src/pages/auth/LoginPage.tsx b/frontend/src/pages/auth/LoginPage.tsx
index 0cec4c5..91400e9 100644
--- a/frontend/src/pages/auth/LoginPage.tsx
+++ b/frontend/src/pages/auth/LoginPage.tsx
@@ -105,7 +105,7 @@ export default function LoginPage() {
                         }
                     }}>
                     <MaterialTextField
-                        label="Имя пользователя"
+                        label="@Имя пользователя"
                         id="login-username"
                         name="username"
                         variant="outlined"
diff --git a/frontend/src/pages/auth/RegisterPage.tsx b/frontend/src/pages/auth/RegisterPage.tsx
index dfc10b8..a119cf0 100644
--- a/frontend/src/pages/auth/RegisterPage.tsx
+++ b/frontend/src/pages/auth/RegisterPage.tsx
@@ -23,6 +23,7 @@ export default function RegisterPage() {
         updateAlerts((alerts) => { alerts.push({type: type, message: message}) });
     }
 
+    const displayNameElement = useRef<TextField>(null);
     const usernameElement = useRef<TextField>(null);
     const passwordElement = useRef<TextField>(null);
     const confirmPasswordElement = useRef<TextField>(null);
@@ -36,11 +37,12 @@ export default function RegisterPage() {
                 <form onSubmit={async (e) => {
                     e.preventDefault();
 
+                    const displayName = displayNameElement.current!.value.trim();
                     const username = usernameElement.current!.value.trim();
                     const password = passwordElement.current!.value.trim();
                     const confirmPassword = confirmPasswordElement.current!.value.trim();
 
-                    if (!username || !password || !confirmPassword) {
+                    if (!displayName || !username || !password || !confirmPassword) {
                         showAlert("danger", "Пожалуйста, заполните все поля");
                         return;
                     }
@@ -50,11 +52,22 @@ export default function RegisterPage() {
                         return;
                     }
 
+                    if (displayName.length < 1 || displayName.length > 64) {
+                        showAlert("danger", "Отображаемое имя должно быть от 1 до 64 символов");
+                        return;
+                    }
+
                     if (username.length < 3 || username.length > 20) {
                         showAlert("danger", "Имя пользователя должно быть от 3 до 20 символов");
                         return;
                     }
 
+                    // Validate username format (only English letters, numbers, dashes, underscores)
+                    if (!/^[a-zA-Z0-9_-]+$/.test(username)) {
+                        showAlert("danger", "Имя пользователя может содержать только английские буквы, цифры, дефисы и подчеркивания");
+                        return;
+                    }
+
                     if (password.length < 5 || password.length > 50) {
                         showAlert("danger", "Пароль должен быть от 5 до 50 символов");
                         return;
@@ -62,6 +75,7 @@ export default function RegisterPage() {
 
                     try {
                         const request: RegisterRequest = {
+                            display_name: displayName,
                             username: username,
                             password: password,
                             confirm_password: confirmPassword
@@ -97,7 +111,18 @@ export default function RegisterPage() {
                     }
                 }}>
                     <MaterialTextField
-                        label="Имя пользователя"
+                        label="Отображаемое имя"
+                        id="register-display-name"
+                        name="display_name"
+                        variant="outlined"
+                        icon="badge--filled"
+                        autocomplete="name"
+                        maxlength={64}
+                        counter
+                        required
+                        ref={displayNameElement} />
+                    <MaterialTextField
+                        label="@Имя пользователя"
                         id="register-username"
                         name="username"
                         variant="outlined"
diff --git a/frontend/src/pages/chat/css/_profile-dialog.scss b/frontend/src/pages/chat/css/_profile-dialog.scss
index a851eb1..bfb9257 100644
--- a/frontend/src/pages/chat/css/_profile-dialog.scss
+++ b/frontend/src/pages/chat/css/_profile-dialog.scss
@@ -55,6 +55,11 @@
         flex-direction: column;
         align-items: center;
 
+        .error-message {
+            color: $color-dark-error;
+            font-size: small;
+        }
+
         .profile-picture-section {
             position: relative;
             display: flex;
@@ -134,15 +139,15 @@
 
         .profile-sections {
             margin: 16px;
-            border-radius: 24px;
             display: flex;
             flex-direction: column;
             gap: 4px;
-            overflow: hidden;
             width: calc(100% - (16px * 2));
             box-sizing: border-box;
 
             .section {
+                $edge-radius: 24px;
+
                 background: $color-dark-surface-container-high;
                 border-radius: 10px;
                 padding: 8px 16px;
@@ -150,6 +155,9 @@
                 flex-direction: row;
                 gap: 16px;
                 align-items: center;
+                transition: outline 0.1s ease;
+                outline: 0px solid transparent;
+                outline-offset: -1px;
 
                 .content-container {
                     display: flex;
@@ -179,6 +187,25 @@
                         }
                     }
                 }
+
+                // First and last section
+                &:first-child {
+                    border-top-left-radius: $edge-radius;
+                    border-top-right-radius: $edge-radius;
+                }
+
+                &:last-child {
+                    border-bottom-left-radius: $edge-radius;
+                    border-bottom-right-radius: $edge-radius;
+                }
+
+                &.error {
+                    outline: 1px solid $color-dark-error;
+
+                    .error-message {
+                        margin-top: 4px;
+                    }
+                }
             }
         }
     }
diff --git a/frontend/src/pages/chat/hooks/useDM.ts b/frontend/src/pages/chat/hooks/useDM.ts
index fbdf108..25ac7fe 100644
--- a/frontend/src/pages/chat/hooks/useDM.ts
+++ b/frontend/src/pages/chat/hooks/useDM.ts
@@ -174,6 +174,7 @@ export function useDM() {
 
                     decryptedMessages.push({
                         id: env.id,
+                        user_id: env.senderId,
                         content: text,
                         username: username,
                         timestamp: env.timestamp,
diff --git a/frontend/src/pages/chat/state.ts b/frontend/src/pages/chat/state.ts
index ca18edb..70ded4f 100644
--- a/frontend/src/pages/chat/state.ts
+++ b/frontend/src/pages/chat/state.ts
@@ -19,6 +19,7 @@ export type CallStatus = "calling" | "connecting" | "active" | "ended";
 export interface ProfileDialogData {
     userId?: number;
     username?: string;
+    display_name?: string;
     profilePicture?: string;
     bio?: string;
     memberSince?: string;
diff --git a/frontend/src/pages/chat/ui/ProfileDialog.tsx b/frontend/src/pages/chat/ui/ProfileDialog.tsx
index e186c25..836279d 100644
--- a/frontend/src/pages/chat/ui/ProfileDialog.tsx
+++ b/frontend/src/pages/chat/ui/ProfileDialog.tsx
@@ -1,20 +1,78 @@
-import { useState, useEffect, useRef, useMemo } from "react";
+import { useState, useEffect, useRef, useMemo, type ReactNode } from "react";
 import { createPortal } from "react-dom";
 import { useAppState } from "@/pages/chat/state";
 import type { ProfileDialogData } from "@/pages/chat/state";
 import defaultAvatar from "@/images/default-avatar.png";
 import { confirm } from "mdui/functions/confirm";
-import { updateProfile, uploadProfilePicture, fetchUserProfile } from "@/core/api/profileApi";
+import { updateProfile, uploadProfilePicture, fetchUserProfileById } from "@/core/api/profileApi";
 import { RichTextArea } from "@/core/components/RichTextArea";
 import { onlineStatusManager } from "@/core/onlineStatusManager";
 import { OnlineStatus } from "./right/OnlineStatus";
 
+interface SectionProps {
+    type: string;
+    icon: string;
+    label: string;
+    error?: string;
+    value?: string;
+    onChange?: (value: string) => void;
+    readOnly: boolean;
+    placeholder: string;
+    textArea?: boolean;
+}
+
+function Section({ type, icon, label, error, value, onChange, readOnly, placeholder, textArea = false }: SectionProps) {
+    let valueComponent: ReactNode = null;
+
+    if (onChange) {
+        if (textArea) {
+            valueComponent = (
+                <RichTextArea
+                    text={value || ""}
+                    onTextChange={onChange}
+                    placeholder={placeholder}
+                    className="value"
+                    rows={1}
+                    readOnly={readOnly}
+                />
+            );
+        } else {
+            valueComponent = (
+                <input
+                className="value"
+                type="text"
+                value={value}
+                onChange={e => onChange(e.target.value)}
+                readOnly={readOnly} />
+            );
+        }
+    } else {
+        valueComponent = (
+            <span className="value">{value}</span>
+        );
+    }
+
+    return (
+        <div className={`section ${type} ${error ? 'error' : ''}`}>
+            <mdui-icon name={icon} />
+            <div className="content-container">
+                <label className="label">{label}</label>
+                {valueComponent}
+                {error && (
+                    <div className="error-message">{error}</div>
+                )}
+            </div>
+        </div>
+    )
+}
+
 export function ProfileDialog() {
-    const { chat, user, closeProfileDialog } = useAppState();
+    const { chat, user, closeProfileDialog, setUser } = useAppState();
     const [isOpen, setIsOpen] = useState(false);
     const [originalData, setOriginalData] = useState<ProfileDialogData | null>(null);
     const [currentData, setCurrentData] = useState<ProfileDialogData | null>(null);
     const [isSaving, setIsSaving] = useState(false);
+    const [errors, setErrors] = useState<{[key: string]: string}>({});
     const fileInputRef = useRef<HTMLInputElement>(null);
     const backdropRef = useRef<HTMLDivElement>(null);
     const dialogRef = useRef<HTMLDivElement>(null);
@@ -40,23 +98,19 @@ export function ProfileDialog() {
         }
     }, [chat.profileDialog, isOpen]);
 
-    const fetchFreshProfileData = async (profileData: ProfileDialogData) => {
+    async function fetchFreshProfileData(profileData: ProfileDialogData) {
         if (!user.authToken) return;
 
         try {
             let freshData = profileData;
 
-            // If it's not the public chat and has a username, fetch fresh data
-            if (profileData.username && profileData.username !== "Общий чат" && profileData.userId) {
-                const userProfile = await fetchUserProfile(user.authToken, profileData.username);
+            // If it's not the public chat and has a user ID, fetch fresh data
+            if (profileData.userId && profileData.username !== "Общий чат") {
+                const userProfile = await fetchUserProfileById(user.authToken, profileData.userId);
                 if (userProfile) {
                     freshData = {
-                        userId: userProfile.id,
-                        username: userProfile.username,
-                        profilePicture: userProfile.profile_picture,
-                        bio: userProfile.bio,
+                        ...userProfile,
                         memberSince: userProfile.created_at,
-                        online: userProfile.online,
                         isOwnProfile: profileData.isOwnProfile
                     };
                 }
@@ -72,7 +126,7 @@ export function ProfileDialog() {
             setCurrentData(profileData);
             setIsOpen(true);
         }
-    };
+    }
 
     // Trigger transition after component mounts
     useEffect(() => {
@@ -90,13 +144,13 @@ export function ProfileDialog() {
 
     // Handle ESC key
     useEffect(() => {
-        const handleEsc = (e: KeyboardEvent) => {
-            if (e.key === "Escape" && isOpen) {
-                handleClose();
-            }
-        };
-
         if (isOpen) {
+            function handleEsc(e: KeyboardEvent) {
+                if (e.key === "Escape") {
+                    handleClose();
+                }
+            }
+
             document.addEventListener("keydown", handleEsc);
             return () => document.removeEventListener("keydown", handleEsc);
         }
@@ -117,6 +171,13 @@ export function ProfileDialog() {
         }
     }, [isOpen, currentData?.userId, currentData?.isOwnProfile]);
 
+    // Validate fields when data changes
+    useEffect(() => {
+        if (currentData && isOpen) {
+            validateFields();
+        }
+    }, [currentData, isOpen]);
+
     const hasChanges = useMemo(() => {
         if (!originalData || !currentData) return false;
 
@@ -127,13 +188,14 @@ export function ProfileDialog() {
         };
 
         return (
+            normalizeValue(originalData.display_name) !== normalizeValue(currentData.display_name) ||
             normalizeValue(originalData.username) !== normalizeValue(currentData.username) ||
             normalizeValue(originalData.bio) !== normalizeValue(currentData.bio) ||
             originalData.profilePicture !== currentData.profilePicture
         );
     }, [originalData, currentData]);
 
-    const handleClose = async () => {
+    async function handleClose() {
         if (hasChanges) {
             try {
                 await confirm({
@@ -151,7 +213,7 @@ export function ProfileDialog() {
         }
     };
 
-    const triggerCloseAnimation = () => {
+    function triggerCloseAnimation() {
         if (backdropRef.current && dialogRef.current) {
             backdropRef.current.classList.remove('open');
             dialogRef.current.classList.remove('open');
@@ -165,29 +227,41 @@ export function ProfileDialog() {
         }
     };
 
-    const handleBackdropClick = (e: React.MouseEvent) => {
+    function handleBackdropClick(e: React.MouseEvent) {
         if (e.target === e.currentTarget) {
             handleClose();
         }
     };
 
-    const handleUsernameChange = (e: React.ChangeEvent<HTMLInputElement>) => {
+    function handleDisplayNameChange(e: React.ChangeEvent<HTMLInputElement>) {
         if (!currentData) return;
-        setCurrentData({ ...currentData, username: e.target.value });
+        const newValue = e.target.value;
+        setCurrentData({ ...currentData, display_name: newValue });
+        
+        // Validate display name in real-time
+        validateDisplayName(newValue);
     };
 
-    const handleBioChange = (newBio: string) => {
+    function handleUsernameChange(value: string) {
+        if (!currentData) return;
+        setCurrentData({ ...currentData, username: value });
+        
+        // Validate username in real-time
+        validateUsername(value);
+    };
+
+    function handleBioChange(newBio: string) {
         if (!currentData) return;
         setCurrentData({ ...currentData, bio: newBio });
     };
 
-    const handleProfilePictureClick = () => {
+    function handleProfilePictureClick() {
         if (currentData?.isOwnProfile) {
             fileInputRef.current?.click();
         }
     };
 
-    const handleFileSelect = (e: React.ChangeEvent<HTMLInputElement>) => {
+    function handleFileSelect(e: React.ChangeEvent<HTMLInputElement>) {
         const file = e.target.files?.[0];
         if (file && file.type.startsWith("image/")) {
             // Open cropper dialog here - for now just update the image
@@ -202,15 +276,60 @@ export function ProfileDialog() {
         }
     };
 
-    const handleSave = async () => {
+    function validateDisplayName(value: string) {
+        let error = "";
+        
+        if (!value || value.trim().length === 0) {
+            error = "Отображаемое имя не может быть пустым";
+        } else if (value.length > 64) {
+            error = "Отображаемое имя не может быть длиннее 64 символов";
+        }
+        
+        setErrors(prev => ({ ...prev, display_name: error }));
+    };
+
+    function validateUsername(value: string) {
+        let error = "";
+        
+        if (!value || value.trim().length === 0) {
+            error = "Имя пользователя не может быть пустым";
+        } else if (value.length < 3) {
+            error = "Имя пользователя должно быть не менее 3 символов";
+        } else if (value.length > 20) {
+            error = "Имя пользователя не может быть длиннее 20 символов";
+        } else if (!/^[a-zA-Z0-9_-]+$/.test(value)) {
+            error = "Имя пользователя может содержать только английские буквы, цифры, дефисы и подчеркивания";
+        }
+        
+        setErrors(prev => ({ ...prev, username: error }));
+    };
+
+    function validateFields() {
+        if (currentData) {
+            validateDisplayName(currentData.display_name || "");
+            validateUsername(currentData.username || "");
+        }
+        
+        return !errors.display_name && !errors.username;
+    };
+
+    async function handleSave() {
         if (!currentData || !user.authToken || !originalData) return;
 
+        // Validate fields first
+        if (!validateFields()) {
+            return;
+        }
+
         setIsSaving(true);
         try {
             // Update profile data
             const updateData: any = {};
+            if (originalData.display_name !== currentData.display_name) {
+                updateData.display_name = currentData.display_name;
+            }
             if (originalData.username !== currentData.username) {
-                updateData.nickname = currentData.username;
+                updateData.username = currentData.username;
             }
             if (originalData.bio !== currentData.bio) {
                 updateData.description = currentData.bio;
@@ -233,22 +352,51 @@ export function ProfileDialog() {
             // Update the original data to match current data
             setOriginalData(currentData);
 
+            // If this is the current user's profile and username was changed, update the current user data
+            if (currentData.isOwnProfile && user.currentUser && user.authToken) {
+                const updatedUser = {
+                    ...user.currentUser,
+                    username: currentData.username || user.currentUser.username,
+                    display_name: currentData.display_name || user.currentUser.display_name,
+                    bio: currentData.bio || user.currentUser.bio,
+                    profile_picture: currentData.profilePicture || user.currentUser.profile_picture
+                };
+                setUser(user.authToken, updatedUser);
+            }
+
             // Close dialog with animation after successful save
             triggerCloseAnimation();
         } catch (error) {
             console.error("Failed to save profile:", error);
+            // Handle API errors
+            if (error instanceof Error && error.message.includes("уже занято")) {
+                setErrors({ username: "Это имя пользователя уже занято" });
+            } else {
+                setErrors({ general: "Ошибка при сохранении профиля" });
+            }
         } finally {
             setIsSaving(false);
         }
-    };
+    }
 
-    const formatDate = (dateString: string) => {
+    function formatDate(dateString: string) {
         return new Date(dateString).toLocaleDateString("ru-RU", {
             year: "numeric",
             month: "long",
             day: "numeric"
         });
-    };
+    }
+
+    const fabVisible = useMemo(() => {
+        let hasErrors = false;
+        Object.values(errors).forEach(error => {
+            if (error) {
+                hasErrors = true;
+            }
+        });
+
+        return hasChanges && currentData?.isOwnProfile && !isSaving && !hasErrors;
+    }, [hasChanges, currentData?.isOwnProfile, isSaving, errors]);
 
     if (!isOpen || !currentData) return null;
 
@@ -281,57 +429,64 @@ export function ProfileDialog() {
                         )}
                     </div>
 
-                    {/* Username */}
-                    {currentData.username && (
-                        <div className="username-section">
-                            <input
-                                className="username-input"
-                                type="text"
-                                value={currentData.username}
-                                onChange={handleUsernameChange}
-                                readOnly={!currentData.isOwnProfile}
-                                placeholder="Имя пользователя"
-                            />
-                        </div>
-                    )}
+                    {/* Display Name */}
+                    <div className={`username-section ${errors.display_name ? 'error' : ''}`}>
+                        <input
+                            className="username-input"
+                            type="text"
+                            value={currentData.display_name}
+                            onChange={handleDisplayNameChange}
+                            readOnly={!currentData.isOwnProfile}
+                            placeholder="Имя"
+                        />
+                        {errors.display_name && (
+                            <div className="error-message">{errors.display_name}</div>
+                        )}
+                    </div>
 
                     {/* Online Status */}
-                    {currentData?.userId && (
+                    {(currentData?.userId || currentData?.isOwnProfile) && (
                         <div className="online-status-section">
-                            <OnlineStatus userId={currentData.userId} />
+                            <OnlineStatus userId={currentData.userId || user.currentUser!.id} />
                         </div>
                     )}
 
                     <div className="profile-sections">
+                        <Section
+                            type="username"
+                            error={errors.username}
+                            icon="alternate_email--filled"
+                            label="Имя пользователя:"
+                            value={currentData.username}
+                            onChange={handleUsernameChange}
+                            readOnly={!currentData.isOwnProfile}
+                            placeholder="username" />
+
+
                         {/* Bio */}
                         {currentData.bio !== undefined && (
-                            <div className="section bio">
-                                <mdui-icon name="info--filled" />
-                                <div className="content-container">
-                                    <label className="label">О себе:</label>
-                                    <RichTextArea
-                                        text={currentData.bio || ""}
-                                        onTextChange={handleBioChange}
-                                        placeholder="Нет информации о себе"
-                                        className="value"
-                                        rows={1}
-                                        readOnly={!currentData.isOwnProfile}
-                                    />
-                                </div>
-                            </div>
+                            <Section
+                                type="bio"
+                                icon="info--filled"
+                                label="О себе:"
+                                value={currentData.bio}
+                                onChange={handleBioChange}
+                                readOnly={!currentData.isOwnProfile}
+                                placeholder="Нет информации о себе"
+                                textArea
+                            />
                         )}
 
                         {/* Member Since */}
                         {currentData.memberSince && (
-                            <div className="section member-since">
-                                <mdui-icon name="calendar_month--filled" />
-                                <div className="content-container">
-                                    <span className="label">Участник с:</span>
-                                    <span className="value">
-                                        {formatDate(currentData.memberSince)}
-                                    </span>
-                                </div>
-                            </div>
+                            <Section
+                                type="member-since"
+                                icon="calendar_month--filled"
+                                label="Участник с:"
+                                value={formatDate(currentData.memberSince)}
+                                readOnly={true}
+                                placeholder="Участник с:"
+                            />
                         )}
                     </div>
                 </div>
@@ -340,7 +495,7 @@ export function ProfileDialog() {
                 {currentData.isOwnProfile && (
                     <mdui-fab
                         icon="check"
-                        className={`profile-dialog-fab ${hasChanges ? "visible" : ""}`}
+                        className={`profile-dialog-fab ${fabVisible ? "visible" : ""}`}
                         onClick={handleSave}
                         disabled={isSaving}
                     />
diff --git a/frontend/src/pages/chat/ui/left/ChatHeader.tsx b/frontend/src/pages/chat/ui/left/ChatHeader.tsx
index fd112a5..ed69d72 100644
--- a/frontend/src/pages/chat/ui/left/ChatHeader.tsx
+++ b/frontend/src/pages/chat/ui/left/ChatHeader.tsx
@@ -13,7 +13,8 @@ export function ChatHeader() {
     const handleProfileClick = () => {
         setProfileDialog({
             userId: user.currentUser?.id,
-            username: profileData?.nickname || "Пользователь",
+            username: profileData?.username || "Пользователь",
+            display_name: profileData?.display_name || "Пользователь",
             profilePicture: profileData?.profile_picture,
             bio: profileData?.description,
             memberSince: user.currentUser?.created_at,
diff --git a/frontend/src/pages/chat/ui/left/ChatTabs.tsx b/frontend/src/pages/chat/ui/left/ChatTabs.tsx
index 729cf55..5733364 100644
--- a/frontend/src/pages/chat/ui/left/ChatTabs.tsx
+++ b/frontend/src/pages/chat/ui/left/ChatTabs.tsx
@@ -1,21 +1,16 @@
 import { useAppState, type ChatTabs } from "@/pages/chat/state";
 import { UnifiedChatsList } from "./UnifiedChatsList";
-import type { FormEvent } from "react";
 import type { Tabs } from "mdui/components/tabs";
 
 export function ChatTabs() {
     const { chat, setActiveTab } = useAppState();
 
-    function handleChange(e: FormEvent<Tabs> & CustomEvent<{ value: string }>) {
-        setActiveTab(e.detail.value as ChatTabs);
-    }
-
     return (
         <div className="chat-tabs">
             <mdui-tabs
                 value={chat.activeTab}
                 full-width
-                onChange={handleChange}>
+                onChange={(e) => setActiveTab((e.target as Tabs).value as ChatTabs)}>
                 <mdui-tab value="chats">
                     Чаты
                 </mdui-tab>
diff --git a/frontend/src/pages/chat/ui/left/UnifiedChatsList.tsx b/frontend/src/pages/chat/ui/left/UnifiedChatsList.tsx
index 4c1bcfa..f076f57 100644
--- a/frontend/src/pages/chat/ui/left/UnifiedChatsList.tsx
+++ b/frontend/src/pages/chat/ui/left/UnifiedChatsList.tsx
@@ -7,7 +7,7 @@ import { fetchUserPublicKey } from "@/core/api/dmApi";
 import type { Message } from "@/core/types";
 import { websocket } from "@/core/websocket";
 import { onlineStatusManager } from "@/core/onlineStatusManager";
-import { OnlineIndicator } from "../right/OnlineIndicator";
+import { OnlineIndicator } from "@/pages/chat/ui/right/OnlineIndicator";
 import defaultAvatar from "@/images/default-avatar.png";
 
 interface PublicChat {
@@ -20,6 +20,7 @@ interface PublicChat {
 interface DMConversation {
     id: number;
     username: string;
+    display_name: string;
     profile_picture?: string;
     online?: boolean;
     type: "dm";
@@ -84,6 +85,7 @@ export function UnifiedChatsList() {
         const dmChatItems: ChatItem[] = dmUsers.map((user: DMUser) => ({
             id: user.id,
             username: user.username,
+            display_name: user.display_name,
             profile_picture: user.profile_picture,
             online: user.online,
             type: "dm" as const,
@@ -172,13 +174,13 @@ export function UnifiedChatsList() {
         };
     }, [allChats]);
 
-    const formatPublicChatMessage = (chatId: string): string => {
+    function formatPublicChatMessage(chatId: string): string {
         const lastMessage = lastMessages[chatId];
         if (!lastMessage) {
             return "";
         }
 
-        const isCurrentUser = lastMessage.username === user.currentUser?.username;
+        const isCurrentUser = lastMessage.user_id === user.currentUser?.id;
         const prefix = isCurrentUser ? "Вы: " : `${lastMessage.username}: `;
 
         const maxContentLength = 50 - prefix.length;
@@ -187,14 +189,13 @@ export function UnifiedChatsList() {
             : lastMessage.content;
 
         return prefix + content;
-    };
+    }
 
-
-    const handlePublicChatClick = async (chatName: string) => {
+    async function handlePublicChatClick(chatName: string) {
         await switchToPublicChat(chatName);
-    };
+    }
 
-    const handleDMClick = async (dmConversation: DMConversation) => {
+    async function handleDMClick(dmConversation: DMConversation) {
         if (!dmConversation.publicKey) {
             const authToken = useAppState.getState().user.authToken;
             if (!authToken) return;
@@ -215,7 +216,7 @@ export function UnifiedChatsList() {
             profilePicture: dmConversation.profile_picture,
             online: dmConversation.online || false
         });
-    };
+    }
 
     if (isLoadingUsers) {
         return (
@@ -256,7 +257,7 @@ export function UnifiedChatsList() {
                     return (
                         <mdui-list-item
                             key={`dm-${chat.id}`}
-                            headline={chat.username}
+                            headline={chat.display_name}
                             onClick={() => handleDMClick(chat)}
                             style={{ cursor: "pointer" }}
                         >
@@ -266,7 +267,7 @@ export function UnifiedChatsList() {
                             <div slot="icon" style={{ position: "relative", width: "40px", height: "40px", display: "inline-block" }}>
                                 <img
                                     src={chat.profile_picture || defaultAvatar}
-                                    alt={chat.username}
+                                    alt={chat.display_name}
                                     style={{
                                         width: "40px",
                                         height: "40px",
diff --git a/frontend/src/pages/chat/ui/right/ChatMessages.tsx b/frontend/src/pages/chat/ui/right/ChatMessages.tsx
index 704b6c6..46f6952 100644
--- a/frontend/src/pages/chat/ui/right/ChatMessages.tsx
+++ b/frontend/src/pages/chat/ui/right/ChatMessages.tsx
@@ -133,7 +133,7 @@ export function ChatMessages({ messages = [], children, isDm = false, onReplySel
                         message={message}
                         isAuthor={isDm ?
                             (message.runtimeData?.dmEnvelope?.senderId === user.currentUser?.id) :
-                            (message.username === user.currentUser?.username)
+                            (message.user_id === user.currentUser?.id)
                         }
                         onContextMenu={handleContextMenu}
                         onReactionClick={handleReactionClick}
@@ -158,7 +158,7 @@ export function ChatMessages({ messages = [], children, isDm = false, onReplySel
                     message={contextMenu.message}
                     isAuthor={isDm ?
                         (contextMenu.message.runtimeData?.dmEnvelope?.senderId === user.currentUser?.id) :
-                        (contextMenu.message.username === user.currentUser?.username)
+                        (contextMenu.message.user_id === user.currentUser?.id)
                     }
                     onEdit={handleEdit}
                     onReply={handleReply}
diff --git a/frontend/src/pages/chat/ui/right/Message.tsx b/frontend/src/pages/chat/ui/right/Message.tsx
index 11afc6d..e864b3b 100644
--- a/frontend/src/pages/chat/ui/right/Message.tsx
+++ b/frontend/src/pages/chat/ui/right/Message.tsx
@@ -10,7 +10,7 @@ import { ecdhSharedSecret, deriveWrappingKey } from "@/utils/crypto/asymmetric";
 import { importAesGcmKey, aesGcmDecrypt } from "@/utils/crypto/symmetric";
 import { getAuthHeaders } from "@/core/api/authApi";
 import { useAppState } from "@/pages/chat/state";
-import { fetchUserProfile } from "@/core/api/profileApi";
+import { fetchUserProfileById } from "@/core/api/profileApi";
 import { ub64 } from "@/utils/utils";
 import { useImmer } from "use-immer";
 import { createPortal } from "react-dom";
@@ -389,10 +389,10 @@ export function Message({ message, isAuthor, onContextMenu, onReactionClick, isD
     };
 
     async function handleProfileClick() {
-        if (!user.authToken || !message.username) return;
+        if (!user.authToken || !message.user_id) return;
 
         try {
-            const userProfile = await fetchUserProfile(user.authToken, message.username);
+            const userProfile = await fetchUserProfileById(user.authToken, message.user_id);
             if (userProfile) {
                 setProfileDialog({
                     ...userProfile,
diff --git a/frontend/src/pages/chat/ui/right/panels/DMPanel.ts b/frontend/src/pages/chat/ui/right/panels/DMPanel.ts
index a94affe..6956d1c 100644
--- a/frontend/src/pages/chat/ui/right/panels/DMPanel.ts
+++ b/frontend/src/pages/chat/ui/right/panels/DMPanel.ts
@@ -7,7 +7,7 @@ import {
     editDmEnvelope,
     deleteDmEnvelope
 } from "@/core/api/dmApi";
-import { fetchUserProfile } from "@/core/api/profileApi";
+import { fetchUserProfileById } from "@/core/api/profileApi";
 import type { DmEncryptedJSON, DmEnvelope, DMWebSocketMessage, EncryptedMessageJson, Message } from "@/core/types";
 import type { UserState, ProfileDialogData } from "@/pages/chat/state";
 import { formatDMUsername } from "@/pages/chat/hooks/useDM";
@@ -84,6 +84,7 @@ export class DMPanel extends MessagePanel {
 
         const dmMsg: Message = {
             id: env.id,
+            user_id: env.senderId,
             content: content,
             username: username,
             timestamp: env.timestamp,
@@ -353,12 +354,13 @@ export class DMPanel extends MessagePanel {
         if (!this.dmData || !this.currentUser.authToken) return null;
 
         try {
-            const userProfile = await fetchUserProfile(this.currentUser.authToken, this.dmData.username);
+            const userProfile = await fetchUserProfileById(this.currentUser.authToken, this.dmData.userId);
             if (!userProfile) return null;
 
             return {
                 userId: userProfile.id,
                 username: userProfile.username,
+                display_name: userProfile.display_name,
                 profilePicture: userProfile.profile_picture,
                 bio: userProfile.bio,
                 memberSince: userProfile.created_at,
diff --git a/frontend/src/pages/chat/ui/right/panels/MessagePanel.ts b/frontend/src/pages/chat/ui/right/panels/MessagePanel.ts
index e46c3c4..805ed8b 100644
--- a/frontend/src/pages/chat/ui/right/panels/MessagePanel.ts
+++ b/frontend/src/pages/chat/ui/right/panels/MessagePanel.ts
@@ -258,6 +258,7 @@ export abstract class MessagePanel {
         const tempId = `temp_${Date.now()}_${Math.random().toString(36).substr(2, 9)}`;
         const tempMessage: Message = {
             id: -1, // Temporary negative ID
+            user_id: this.currentUser.currentUser?.id ?? -1,
             username: this.currentUser.currentUser?.username ?? "You",
             content: content.trim(),
             is_read: false,
diff --git a/frontend/src/pages/chat/ui/right/panels/PublicChatPanel.ts b/frontend/src/pages/chat/ui/right/panels/PublicChatPanel.ts
index 3eae929..d8c0e7f 100644
--- a/frontend/src/pages/chat/ui/right/panels/PublicChatPanel.ts
+++ b/frontend/src/pages/chat/ui/right/panels/PublicChatPanel.ts
@@ -121,7 +121,7 @@ export class PublicChatPanel extends MessagePanel {
                     const newMsg = response.data;
 
                     // Check if this is a confirmation of a message we sent
-                    const isOurMessage = newMsg.username === this.currentUser.currentUser?.username;
+                    const isOurMessage = newMsg.user_id === this.currentUser.currentUser?.id;
                     if (isOurMessage) {
                         // This is our message being confirmed, find the temp message and replace it
                         const tempMessages = this.getMessages().filter(m => m.id === -1 && m.runtimeData?.sendingState?.tempId);
@@ -199,7 +199,8 @@ export class PublicChatPanel extends MessagePanel {
 
     async getProfile(): Promise<ProfileDialogData | null> {
         return {
-            username: "Общий чат",
+            username: "general",
+            display_name: "Общий чат",
             bio: "Общаемся со всеми пользователями FromChat!",
             isOwnProfile: false
         };