“I was always getting into scuffles with my brothers when I grew up. One time a small band of raiders attacked Junktown, and I beat one into submission before he could get his gun on me. Just luck, really, but Gizmo was sponsoring organized fights, and I needed some money. Been boxing ever since.”
Saul was raised in Junktown, having stayed there for his whole life. For a long time, he lived with his brothers, being somewhat of a guardian to them, as they lived a poor life. One day, when Raiders attacked them, he "kicked one of their asses pretty good" (into submission). Gizmo, eying his talent, employed him in the boxing ring.
Saul gets his money from bets in the ring. In dialogue, he mentions his two brothers: James, who died in a raider attack; and Darrell, who left Junktown one day to find "the treasures of the ancients." He is referring to stories the Brotherhood made up about the Glow, but cannot offer directions for the player.
Help Saul: If one helps Saul's girlfriend Trish by killing Shark in the Skum Pitt, they will trigger the quest. The quest can be completed by talking to him, where he will thank and reward with experience points.
The Vault Dweller can bet on the outcome of Saul's boxing matches, either Saul or his challenger. The odds of winning are not good, even if one bets on Saul, who has the upper hand. A few of Saul's competitors in the ring have been a man wearing metal armor and, quite oddly, a radscorpion.