Billy Black is the wheelchair-bound father of Jacob Black. In the first book he seems to hate the Cullens. I couldn't imagine why.. *sarcasm hand raised *. He and Charlie Swan have a case of Guy Love, Between Two Guys.
Since being a cringe-worthy Native American stereotype is a full-time job (and he doesn't appear to have a real job), he does not have much time to help the plot along. He exists to give Bella Sue grim warnings about the Cullens (for unfathomable reas
ons however, he congratulates Bella when she marries Edward in Breaking Dawn, despite the fact she married a sparkling statue and broke his son's heart at the same time. Maybe that's because she will live with Eddie now and he can visit Charlie whenever he wants, encourage Jacob (his son) to force himself on Bella, and also it was his truck Bella gets from her father.
Perhaps Smeyer just wanted to make (poor) use of her severely underused minor characters, but it is noted that in Eclipse, it was mentioned that Billy Black is a potential candidate for being Embry's father, this meaning that he could have cheated on his wife. Yet another one of those beautiful moral messages that Smeyer conveys through the Twilight saga.