Silas (Fallout 3)

 is a slaver stationed at the Lincoln Memorial. He is likely the lieutenant or underling of Leroy Walker. He is involved in the Head of State quest.

Interactions with the player character
When approaching the Memorial, Silas will stop the Lone Wanderer from heading up the stairs, and informs them that the Memorial is "off-limits". If asked, he will lead you to his superior, Leroy Walker, who is stationed inside the Memorial Office.