Defender Sibley

 is a member of the Outcasts located at the Outcast Outpost at Bailey's Crossroads.

Once the player completes the Anchorage simulation and opens the locked door to the armory, Sibley will attempt a coup d'etat with his men against Protector McGraw, feeling that you don't deserve anything in the chamber.

Related quests

 * Aiding the Outcasts

Appearances
only appears in the Fallout 3 Operation: Anchorage DLC.