Jonathan Maxson is the father of Arthur Maxson and husband of Jessica Maxson. He and his wife died when their son was still very young, making Arthur the last of the Maxson Dynasty at the time of Fallout 3. The cause of his death is not specified.
Jonathan is not only a descendant of Roger Maxson, the founder of the Brotherhood of Steel, but he was also a high-ranking Paladin just outside New California Republic. He was, however, killed in battle.