In 2155, while hunting down a group of Raiders known as the Vipers, Maxson (who was unhelmeted at the time) was grazed in the head by an arrow. A deadly Viper poison killed him within hours.”— Lyons' Brotherhood of Steel scribes
He was only a teenager in 2077, during the Exodus of the Mariposa Military Base soldiers to the Lost Hills bunker. His mother died during the Exodus. In 2135, Roger Maxson died of cancer, and his son took over as the High Elder of the Brotherhood.
In 2155, The Brotherhood sent out a few squads of scouts to track down a raider gang known as the Vipers - it was more of a training exercise conducted by the High Elder, as the Brotherhood was convinced that small detachment of troops in power armor would be sufficient to deal with a group of raiders, no matter how large. One Brotherhood squad, led by Maxson, found the Vipers. Expecting the raiders to break and run, Maxson didn't take into account the religious ferocity of the Vipers (or their poisoned weapons), and when a single arrow nicked him with his helmet off, he died within hours. John Maxson, his son, took up the role of Elder, and Rhombus became the new head of the Paladins.