Bill is the sole survivor living in the abandoned town of Lincoln in The Last of Us. He is obsessive-compulsive, adhering to a strict order of living to ensure his survival in the cordyceps-infested town. He has traps set up all over the place to keep away both the Infected and would-be scavengers. Apart from having sporadic communication with Joel and Tess to smuggle goods through his territory in exchange for supplies, he has very little contact with human life. This isolation seems to have taken a toll on his psyche, as he talks to himself a lot and he has to be forced to lend a helping hand to passersby.
He and Ellie share very contentious moments throughout the course of their interactions, with her curious and confrontational attitude at odds with his extremely regimented lifestyle.
He had a partner named Frank, both of them doing what they could to survive in Lincoln, until they had a falling out and separated ways before the events of the game.