diff --git a/lib/irc/handler.ex b/lib/irc/handler.ex
index d1aadbc..16aac76 100644
--- a/lib/irc/handler.ex
+++ b/lib/irc/handler.ex
@@ -1072,10 +1072,9 @@ defmodule M51.IrcConn.Handler do
             fn _room_id, room ->
               commands =
                 room.members
-                |> Stream.map(fn {user_id, _member} ->
+                |> Stream.map(fn {user_id, member} ->
                   [local_name, hostname] = String.split(user_id, ":", parts: 2)
-                  # TODO: pick the most common display name of the user instead
-                  gecos = user_id
+                  gecos = member.display_name || user_id
                   # RPL_WHOREPLY
                   make_numeric.("352", [
                     target,
@@ -1097,9 +1096,9 @@ defmodule M51.IrcConn.Handler do
         else
           # target is a nick
           [local_name, hostname] = String.split(target, ":", parts: 2)
+          display_name = M51.MatrixClient.State.user_display_name(matrix_state, target)
 
-          # TODO: pick the most common display name instead
-          gecos = target
+          gecos = display_name
 
           send_batch.(
             [
@@ -1133,10 +1132,10 @@ defmodule M51.IrcConn.Handler do
             end
 
           [local_name, hostname] ->
-            [member: memberships] = M51.MatrixClient.State.user(matrix_state, target)
+            memberships = M51.MatrixClient.State.user_memberships(matrix_state, target)
+            display_name = M51.MatrixClient.State.user_display_name(matrix_state, target)
 
-            # TODO: pick the most common display name instead
-            gecos = target
+            gecos = display_name
 
             overhead =
               make_numeric.("353", [target, ""]) |> M51.Irc.Command.format() |> byte_size()
@@ -1148,7 +1147,6 @@ defmodule M51.IrcConn.Handler do
 
             channel_commands =
               memberships
-              |> Map.keys()
               |> Enum.map(fn room_id ->
                 M51.MatrixClient.State.room_irc_channel(matrix_state, room_id)
               end)
diff --git a/lib/matrix_client/state.ex b/lib/matrix_client/state.ex
index 58d8334..4a35cce 100644
--- a/lib/matrix_client/state.ex
+++ b/lib/matrix_client/state.ex
@@ -95,7 +95,8 @@ defmodule M51.MatrixClient.State do
       room = Map.get(state.rooms, room_id, @emptyroom)
 
       if Map.has_key?(room.members, userid) do
-        {true, state}
+        # User may have changed their display-name, so update the member list
+        {true, update_in(state.rooms[room_id].members[userid], fn _ -> member end)}
       else
         room = %{room | members: Map.put(room.members, userid, member)}
         {false, %{state | rooms: Map.put(state.rooms, room_id, room)}}
@@ -120,18 +121,32 @@ defmodule M51.MatrixClient.State do
   end
 
   @doc """
-    Returns [member: %{room_id => %M51.Matrix.RoomMember{...}}]
+    Returns the user's current display name. This is the same across all rooms
+    they're in, but not guaranteed to be unique vs. other users.
+
+    If the user has no known display name (i.e. membership set is empty), just
+    returns the userid.
+  """
+  def user_display_name(pid, user_id) do
+    Agent.get(pid, fn state ->
+      state.rooms
+        |> Stream.filter(fn {_room_id, room} -> Map.has_key?(room.members, user_id) end)
+        |> Stream.map(fn {_room_id, room} -> room.members[user_id].display_name end)
+        # Matrix display names are per-user, so we just pick an arbitrary channel
+        # that they're in and fish it out of the userlist.
+        # TODO: store a user_id to user info map separately from the channels?
+        |> Enum.at(0, user_id)
+    end)
+  end
+
+  @doc """
+    Returns a list of room_ids that the user is a member in.
   """
-  def user(pid, user_id) do
+  def user_memberships(pid, user_id) do
     Agent.get(pid, fn state ->
-      [
-        member:
-          state.rooms
-          |> Map.to_list()
-          |> Enum.map(fn {room_id, room} -> {room_id, Map.get(room.members, user_id)} end)
-          |> Enum.filter(fn {_room_id, member} -> member != nil end)
-          |> Map.new()
-      ]
+      state.rooms
+      |> Enum.filter(fn {_room_id, room} -> Map.has_key?(room.members, user_id) end)
+      |> Enum.map(fn {room_id, _room} -> room_id end)
     end)
   end
 
diff --git a/test/irc/handler_test.exs b/test/irc/handler_test.exs
index 4c33d21..9dbd041 100644
--- a/test/irc/handler_test.exs
+++ b/test/irc/handler_test.exs
@@ -762,7 +762,7 @@ defmodule M51.IrcConn.HandlerTest do
     assert line == "@label=l2 BATCH +#{batch_id} :labeled-response\r\n"
 
     assert_line(
-      "@batch=#{batch_id} :server. 352 foo:example.org #existing_room:example.org user1 example.org * user1:example.org H :0 user1:example.org\r\n"
+      "@batch=#{batch_id} :server. 352 foo:example.org #existing_room:example.org user1 example.org * user1:example.org H :0 user one\r\n"
     )
 
     assert_line(
@@ -788,7 +788,7 @@ defmodule M51.IrcConn.HandlerTest do
     send(handler, cmd("WHO #existing_room:example.org"))
 
     assert_line(
-      ":server. 352 foo:example.org #existing_room:example.org user1 example.org * user1:example.org H :0 user1:example.org\r\n"
+      ":server. 352 foo:example.org #existing_room:example.org user1 example.org * user1:example.org H :0 user one\r\n"
     )
 
     assert_line(
@@ -826,7 +826,7 @@ defmodule M51.IrcConn.HandlerTest do
     assert line == "@label=l1 BATCH +#{batch_id} :labeled-response\r\n"
 
     assert_line(
-      "@batch=#{batch_id} :server. 311 foo:example.org user1:example.org user1 example.org * :user1:example.org\r\n"
+      "@batch=#{batch_id} :server. 311 foo:example.org user1:example.org user1 example.org * :user one\r\n"
     )
 
     assert_line(