From his computer (which the Lone Wanderer can hack without Karma penalties), the Lone Wanderer can discover that young Arthur enjoys writing stories, has a crush on Sarah Lyons (because she taught him to kill a man by stabbing him in the kidneys), and that there is a Guns and Bullets magazine underneath a bed in the den.
After the events of Fallout 3 the East Coast Brotherhood of Steel faced a leadership crisis after Elder Owyn Lyons died of natural causes and his daughter Sarah Lyons was killed in combat shortly afterwards. The East Coast Brotherhood repeatedly appointed and deposed several ineffectual Elders until Arthur Maxson was appointed Elder of the East Coast Brotherhood by the West Coast Elders in 2283 at the age of 16, after displaying exceptional skill as a capable warrior and diplomat by defeating the supermutant leader Shepherd and brokering peace with the Brotherhood Outcasts, bringing them back into the fold.
Arthur returns in Fallout 4 as a twenty-year-old, fully trained and the leader of the Brotherhood in the East Coast. After reuniting the outcasts with the Brotherhood of Steel at the age of 16, Arthur holds the position of Elder, the youngest in the history of the Brotherhood, and is torn between the ways of his predecessor: Elder Lyons, using technology to help others or the traditional Brotherhood approach by seizing any advanced technology they can as his chapter prepares to go to war with the Institute.
A charismatic leader and a skilled tactician, Arthur has won the respect and admiration of his men through his numerous exploits. He owes his scar to a fight that he led alone against a deathclaw, an opponent that even BoS veterans advise not to face single-handedly.
"Oh, well... You see, I am descended from the great Roger Maxson, founder of our order. I am the last of his line. They say my soul was forged from eternal steel, but I don't believe that. I'm really just a normal boy."
"I did go out one time, you know! Sarah... Um... Sentinel Lyons took me out. Just to show me. I killed a Super Mutant, too! I swear! I, um... I also sort of shot Sarah. But just a little! It was just a flesh wound..."