Arthur Maxson

 is the last descendant of the Maxson dynasty, the founders and traditional leaders of the Brotherhood of Steel. He was born in 2267 to Jonathan and Jessica who are both deceased at the time of Fallout 3. Still a child and ranked as Squire, he has been placed under the supervision of Elder Owyn Lyons. Due to internal conflicts in the Brotherhood of Steel this move was thought to increase his personal safety; he is considered to be safer in the Citadel than in the Brotherhood's homelands, even though it is located in enemy territory.

He can usually be found in the Citadel's B-Ring where his room (and personal terminal) is located.

One of his dialogue lines is what links the FO3 Enclave Power Armor to previous Fallout games' "Advanced Power Armor Mk II". He is also the only character, besides Star Paladin Cross, who recites lines from the Codex.

From his computer (which you can hack without Karma penalties), you can find that under a bed in the Den, there is a Guns and Bullets magazine and he has a crush in Sarah Lyons.

Appearances
Squire  appears only in Fallout 3.

Behind the scenes
 is likely a recreation of Arthur Pendragon. He is the rightful heir to the Brotherhood of Steel, but has been sent to live with a foster father for his safety. His Kingdom is divided and the factions cannot agree upon a leader. Arthur Maxson is being trained in the ideal of might for right, which his Kingdom has never followed.