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 super mutant leader Shephard 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 has established an amalgam between the ways of his predecessor and tutor Elder Owyn Lyons, who was using technology to help others, and the traditional Brotherhood approach of coveting and preserving advanced technology to protect people from abusing it. As a result, he is much more lenient about technology being in the hands of outsiders, and allocates teams of soldiers to combat dangers that would otherwise harm or kill the people of the wasteland, while he has other teams scouring the ruins for technology that could be misused in the wrong hands. Maxson also 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 13, 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 dislike. The Western Elders have these cults hunted down and uprooted.
He deeply cares for everyone under his command, as he was heavily reluctant to allow Ingram into the field as a field scribe despite Knight-Captain Cade's professional opinion that due to her power armor frame (which replaced her legs and much of her lower torso), she was more suited for combat than scribe-work, in fact probably better suited than any Knight they could muster. Additionally, he explicitly ordered that all technology was to be traded for food and medicine, and violent confrontation was to be a last resort, which drastically sets him apart from the West Coast Brotherhood, who used violence as a first resort. It shows not only that he doesn't wish to risk the lives under his command, but he does genuinely care about the people of the Commonwealth.
If, however, the player decides to side with the Institute, then during the quest Airship Down he will emerge from a crashed Vertibird as the only survivor, in his personal Elder Power Armor wielding his unique Gatling laser. The player will have no choice but to either kill him or serve as a distraction from the Synth Virus, and after Liberty Prime is infected with the Institute virus, Liberty Prime will either instantly kill Maxson (all of his attacks are instant kills) or he will lead the fragmented Brotherhood back south if Prime happens to miss him in the firefight and he survives the following firefight.
In the Minutemen main quests, he serves as a mentioned only antagonist, as Maxson is killed when their artillery blows the Prydwen out of the sky.
In the Railroad main quests he is largely mentioned only until Rockets' Red Glare, where he can be confronted while or after sabotaging the Prydwen.
If the Brotherhood is victorious, then Maxson will advise that, as the Sole Survivor holds the rank of Sentinel, while they are free to carry out their own missions, to keep the Brotherhood's interests as a whole at heart.
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.
Maxson is one of only two characters in Fallout 3 who will recite excerpts from the Codex; the other is Star Paladin Cross.
The T-60 power armor Maxson wears during Airship Down only is upgraded to the highest tier F and bears the unique Elder paint job. This paint scheme cannot be crafted by the Sole Survivor, so it is lost forever if the player decides to recolor the armor parts after acquiring them. PC players who inadvertently did that, failed to loot the armor during Airship Down or led someone other than the Institute to victory can add it to their inventory with the command player.additem 197994.
It is impossible to pickpocket Maxson, even with the level 4 Pickpocket perk.
When fighting Maxson during the Airship Down, there is a possibility of gaining a unique power armor frame called "Elder Maxson's Power Armor" by shooting the fusion core out of his suit. This has no unique effects, but it is the only named power armor frame in the base game.
Arthur Maxson's rise to power has some similarities with the Arthur of legend. After Uther's demise, the young Arthur, at age fifteen, became the new King of Britain and fought a succession of battles, eventually leading to the Battle of Bath. Arthur is victorious against the Picts and Scots before establishing an empire. Similarly, some time after Sarah Lyons' demise, at age fifteen, Arthur Maxson fights a series of battles against the super mutants, eventually leading to his battle against the super mutant Shephard who was attempting to unite the super mutants of the Capital Wasteland. His victories lead to his ascension as elder of the eastern chapter, and establishing Brotherhood territory on the east coast.
Maxson's concept art shows him a bit different than how he appears in game. At one point he was intended to have been clean shaven and to have had a cape rather than his battle coat.
"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..."
"You truly have become one of us, sister/brother." (Said in response to the Sole Survivor after telling him they defeated Institute for the people of the Commonwealth.)
"Our mission in the Commonwealth is clear: the Institute and its technologies must be destroyed in order to preserve our future. Which leaves me facing the most difficult order I've ever given."
"Brothers and Sisters, the road behind us has been long and fraught with difficulty. Each and every one of you has surpassed my expectations by rapidly facilitating our arrival in the Commonwealth. You have accomplished this amazing feat without a hint of purpose or direction, and most impressively, without question. Now that the ship is in position, it is the time to reveal our purpose and our mission. Beneath the Commonwealth, there is a cancer known as "The Institute", a malignant growth that needs to be cut before it infects the surface. They are experimenting with dangerous technologies that could prove to be the world’s undoing for the second time in recent history. The Institute Scientists have created a weapon that transcends the destructive nature of the atom bomb. They call their creation the "synth", a robotic abomination of technology that is free-thinking and masquerades as a human being. This notion that a machine can be granted free will is not only offensive, but horribly dangerous. And like the atom, if it isn’t harnessed properly, it has the potential of rendering us extinct as a species. I am not prepared to allow the Institute to continue this line of experimentation. Therefore, the Institute and their "synths" are considered enemies of the Brotherhood of Steel, and should be dealt with swiftly and mercilessly. This campaign will be costly and many lives will be lost. But in the end, we will be saving humankind from its worst enemy... itself. Ad Victoriam!"