diff --git a/apps/desktop/src/components/CallParticipantTile.tsx b/apps/desktop/src/components/CallParticipantTile.tsx
index 6ea808c..3d1f3d7 100644
--- a/apps/desktop/src/components/CallParticipantTile.tsx
+++ b/apps/desktop/src/components/CallParticipantTile.tsx
@@ -1,5 +1,6 @@
 import { useEffect, useRef } from 'react';
 
+import { useNickname } from '../lib/friendNicknames';
 import {
   CrownIcon,
   HeadphonesOffIcon,
@@ -89,6 +90,7 @@ export interface ParticipantTileProps {
 
 export function CallParticipantTile(props: ParticipantTileProps) {
   const {
+    userId,
     displayName,
     me,
     muted,
@@ -107,6 +109,13 @@ export function CallParticipantTile(props: ParticipantTileProps) {
     onContextMenu,
   } = props;
 
+  // Apply the per-viewer nickname override once at the top — each tile is
+  // already per-participant, so a single hook call is fine. The resolved
+  // name is forwarded into the avatar sub-components below so their initial
+  // letter respects the nickname too.
+  const resolvedName = useNickname(userId, displayName);
+  const tileProps = { ...props, displayName: resolvedName };
+
   const small = size === 'small';
   // Discord-style: full tile border switches to emerald the whole time the
   // user is speaking. Same treatment for audio + video tiles so the visual
@@ -132,9 +141,9 @@ export function CallParticipantTile(props: ParticipantTileProps) {
       }
     >
       {video ? (
-        <VideoStub {...props} small={small} fit={focused ? 'contain' : 'cover'} />
+        <VideoStub {...tileProps} small={small} fit={focused ? 'contain' : 'cover'} />
       ) : (
-        <AudioContent {...props} small={small} />
+        <AudioContent {...tileProps} small={small} />
       )}
 
       {speaking && (
@@ -187,7 +196,7 @@ export function CallParticipantTile(props: ParticipantTileProps) {
             />
           )}
           <span className="truncate">
-            {displayName}
+            {resolvedName}
             {me ? ' (du)' : ''}
           </span>
           {e2ee && (
diff --git a/apps/desktop/src/components/ConversationHeader.tsx b/apps/desktop/src/components/ConversationHeader.tsx
index 829504f..0215a83 100644
--- a/apps/desktop/src/components/ConversationHeader.tsx
+++ b/apps/desktop/src/components/ConversationHeader.tsx
@@ -3,6 +3,7 @@ import type { PresenceState } from '@chat-app/shared/supabase';
 import { useTranslation } from 'react-i18next';
 
 import { useCall } from '../context/CallContext';
+import { useNickname } from '../lib/friendNicknames';
 import type { PeerPresence } from '../lib/usePeerPresence';
 import { Avatar } from './Avatar';
 import {
@@ -79,7 +80,13 @@ function HeaderBar({
   const { t } = useTranslation(['app']);
 
   const isDm = conversation.type === 'dm';
-  const title = isDm ? (conversation.peer?.displayName ?? '?') : (conversation.name ?? '?');
+  // For DMs, route the peer's display name through the per-viewer nickname
+  // override. Falls back to the real displayName when no nickname is set.
+  const peerName = useNickname(
+    conversation.peer?.userId,
+    conversation.peer?.displayName ?? '?',
+  );
+  const title = isDm ? peerName : (conversation.name ?? '?');
   const handle = isDm ? '@' + (conversation.peer?.username ?? '?') : '';
   const peerAvatar = isDm
     ? (conversation.peer?.avatarUrl ?? null)
diff --git a/apps/desktop/src/components/MentionAutocomplete.tsx b/apps/desktop/src/components/MentionAutocomplete.tsx
index c896438..5bdf96e 100644
--- a/apps/desktop/src/components/MentionAutocomplete.tsx
+++ b/apps/desktop/src/components/MentionAutocomplete.tsx
@@ -1,8 +1,11 @@
 import type { ConversationSummary } from '@chat-app/shared/chat';
 import { useEffect, useState } from 'react';
 
+import { useNickname } from '../lib/friendNicknames';
 import { Avatar } from './Avatar';
 
+type Member = ConversationSummary['members'][number];
+
 interface Props {
   members: ConversationSummary['members'];
   query: string;
@@ -63,37 +66,58 @@ export function MentionAutocomplete({ members, query, excludeUserId, onSelect, o
       aria-label="Mitglieder"
       className="absolute bottom-full left-0 right-0 z-20 mb-2 max-h-64 overflow-y-auto rounded-xl border border-line bg-surface-2 p-1 shadow-xl dark:bg-[#2b2d31]"
     >
-      {matches.map((m, idx) => {
-        const name = m.profile?.displayName ?? m.profile?.username ?? '?';
-        const handle = m.profile?.username ?? '';
-        const isActive = idx === active;
-        return (
-          <button
-            key={m.userId}
-            type="button"
-            role="option"
-            aria-selected={isActive}
-            onMouseEnter={() => setActive(idx)}
-            onClick={() => {
-              if (m.profile?.username) onSelect(m.profile.username);
-            }}
-            className={
-              'flex w-full cursor-pointer items-center gap-2 rounded-lg px-2 py-1.5 text-left text-sm transition ' +
-              (isActive
-                ? 'bg-accent/20 text-fg'
-                : 'text-fg-muted hover:bg-surface-3 dark:hover:bg-[#383a40]')
-            }
-          >
-            <Avatar
-              displayName={name}
-              url={m.profile?.avatarUrl ?? null}
-              className="h-6 w-6 text-[10px]"
-            />
-            <span className="min-w-0 flex-1 truncate text-fg">{name}</span>
-            <span className="shrink-0 text-[10px] text-fg-muted">@{handle}</span>
-          </button>
-        );
-      })}
+      {matches.map((m, idx) => (
+        <MemberRow
+          key={m.userId}
+          member={m}
+          isActive={idx === active}
+          onActivate={() => setActive(idx)}
+          onSelect={onSelect}
+        />
+      ))}
     </div>
   );
 }
+
+// Extracted per-row component so we can call `useNickname` once per member
+// at the top of THIS component (hooks can't run inside .map callbacks).
+function MemberRow({
+  member,
+  isActive,
+  onActivate,
+  onSelect,
+}: {
+  member: Member;
+  isActive: boolean;
+  onActivate: () => void;
+  onSelect: (username: string) => void;
+}) {
+  const fallback = member.profile?.displayName ?? member.profile?.username ?? '?';
+  const name = useNickname(member.userId, fallback);
+  const handle = member.profile?.username ?? '';
+  return (
+    <button
+      type="button"
+      role="option"
+      aria-selected={isActive}
+      onMouseEnter={onActivate}
+      onClick={() => {
+        if (member.profile?.username) onSelect(member.profile.username);
+      }}
+      className={
+        'flex w-full cursor-pointer items-center gap-2 rounded-lg px-2 py-1.5 text-left text-sm transition ' +
+        (isActive
+          ? 'bg-accent/20 text-fg'
+          : 'text-fg-muted hover:bg-surface-3 dark:hover:bg-[#383a40]')
+      }
+    >
+      <Avatar
+        displayName={name}
+        url={member.profile?.avatarUrl ?? null}
+        className="h-6 w-6 text-[10px]"
+      />
+      <span className="min-w-0 flex-1 truncate text-fg">{name}</span>
+      <span className="shrink-0 text-[10px] text-fg-muted">@{handle}</span>
+    </button>
+  );
+}
diff --git a/apps/desktop/src/components/MessageBubble.tsx b/apps/desktop/src/components/MessageBubble.tsx
index 9945171..6556312 100644
--- a/apps/desktop/src/components/MessageBubble.tsx
+++ b/apps/desktop/src/components/MessageBubble.tsx
@@ -10,6 +10,7 @@ import { createPortal } from 'react-dom';
 import { useTranslation } from 'react-i18next';
 
 import { useAuth } from '../context/AuthContext';
+import { useNickname } from '../lib/friendNicknames';
 import { ensureInstallId } from '../lib/installId';
 import { supabase } from '../lib/supabase';
 import { cachedUserKey } from '../lib/userIdentity';
@@ -100,6 +101,12 @@ export function MessageBubble({
   const { t } = useTranslation(['app']);
   const { session } = useAuth();
 
+  // Per-viewer nickname override for the message sender. Fallback chain
+  // keeps the existing behavior when no nickname is set. Skipped for the
+  // quoted-sender snippet — that's a different user.
+  const senderName = useNickname(message.senderId, senderDisplayName ?? '');
+  const resolvedSenderDisplayName = senderName.length > 0 ? senderName : null;
+
   const parsed = parseMessagePayload(message.plaintext);
   const initialText = parsed.kind === 'text' ? parsed.text : '';
   const initialAttachments = parsed.kind === 'text' ? parsed.attachments : [];
@@ -281,7 +288,7 @@ export function MessageBubble({
         <AvatarSlot
           show={isLastOfRun}
           url={senderAvatarUrl ?? null}
-          displayName={senderDisplayName ?? null}
+          displayName={resolvedSenderDisplayName}
           {...(onAvatarClick
             ? { onClick: (ev: React.MouseEvent) => onAvatarClick(message.senderId, ev) }
             : {})}
@@ -299,7 +306,7 @@ export function MessageBubble({
         parsed={parsed}
         mine={mine}
         time={time}
-        senderDisplayName={senderDisplayName ?? null}
+        senderDisplayName={resolvedSenderDisplayName}
       />
     );
   }
@@ -315,7 +322,7 @@ export function MessageBubble({
       <AvatarSlot
         show={isLastOfRun}
         url={senderAvatarUrl ?? null}
-        displayName={senderDisplayName ?? null}
+        displayName={resolvedSenderDisplayName}
         {...(onAvatarClick
           ? { onClick: (ev: React.MouseEvent) => onAvatarClick(message.senderId, ev) }
           : {})}