Mr. Keller is the head of the Keller family, which took refuge in the locked armory bunker of the National Guard depot.
Similar to the other members of the Keller family, he holds one of the numbers of a password that allowed entrance to the shelter. His daughter mentions in her diary that he frequently left the safety of the bunker. He appears as a glowing one upon the Lone Wanderer's arrival.
Mr. Keller appears only in Fallout 3.