Ephraim Black

Ephraim Black was the last Quileute chief and leader of a pack of three werewolves: himself, Levi Uley, and Quil Ateara I. He is the grandfather of Billy Black, and the great-grandfather of Jacob Black, Rebecca Black and Rachel Black.

History
Sometime during Ephraim's life, a coven of vampires, the Cullen family, came to live in Forks, near the Quileute reservation of La Push where Ephraim lived. By nature, the shape-shifters and Cullens were enemies, and the vampires' presence in the area made Ephraim and two other Quileutes, Levi Uley and Quil Ateara I, phase into wolves. The wolves prepared to fight the vampires off but Carlisle, the coven's leader, was able to negotiate a peace treaty with them: as long as the Cullens didn't bite any humans or come on to the Quileute's land, the werewolves wouldn't attack them or reveal their presence to the humans.

Ephraim's descendant, Jacob, was the one who violated the treaty Ephraim made when he revealed that the Cullens were vampires to his friend Bella Swan. In Breaking Dawn, the treaty was flouted once again with Jacob's permission, to allow Edward Cullen to save Bella from death by contaminating her with vampire venom. Thhe treaty was permanently dissolved or at least modified due to Jacob Black imprinting on Renesmee Cullen.

Etymology
Ephraim means "fruitful."

Trivia

 * While Ephraim doesn't make an appearance in the book series (due to the fact that he died before the series starts), it is highly likely that the Quileute who appeared in the flashback sequence in the Twilight film was him.
 * There has been some speculation among fans that Billy Black is really Ephraim. Stephenie Meyer, however, has said that Billy really is Ephraim's grandson.