Look around you! Look at the scorched earth and the bones that litter the wasteland. Millions... perhaps even billions, died because science outpaced man's restraint! They called it a "new frontier" and "pushing the envelope," completely disregarding the repercussions. Can't you see the same thing is happening again?
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 thereafter. The East Coast Brotherhood repeatedly appointed and deposed numerous ineffectual Elders until Arthur Maxson was appointed Elder of the East Coast Brotherhood by the West Coast Elders in 2283 at the age of sixteen, the youngest in the history of the Brotherhood, 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 the young and idealistic, but capable leader of the Brotherhood in the East Coast. He is torn between the ways of his predecessor Elder Lyons, using technology to help others, and the traditional Brotherhood approach of coveting and preserving advanced technology to protect people from abusing it. Despite this he still strongly insists that the Brotherhood has the best interests of the Commonwealth in mind.
As a charismatic leader and a skilled tactician, Arthur has won the respect and admiration of his men through his numerous exploits. When he was 10 he killed a Super Mutant in a training mission. He owes his scar to a fight that he led alone against a deathclaw at the age of 14, an opponent that even BoS veterans advise not to face single-handedly.
Maxson is loved and admired throughout the Brotherhood. On the West Coast some in the Brotherhood have even gone so far as to worship Maxson, much to his disliking, forming cults that are hunted down and uprooted on Maxson's orders.
Tour of Duty: After Paladin Danse brings the Sole Survivor to the Prydwen after its arrival in the Commonwealth, Maxson promotes them to the rank of Knight and asks them to tour the Prydwen and get to know her crew.
"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..."