- "My great grandfather, the Chief, found them hunting on our land. But they claimed to be something different, so we made a treaty with them. If they promised to stay off the Quileute lands, then we wouldn't expose them to what they really were... to the pale-faces."
- ―Jacob Black on his great-grandfather[src]
Ephraim Black was a Quileute chief and Alpha of a pack of three shape-shifters: himself, Levi Uley, and Quil Ateara II. He was the husband of Martha Young, the grandfather of Billy, Nora, Jennie, Connie and Emmie Black, the grandfather-in-law of Sarah Black and Kevin Littlesea, the great-grandfather of Jacob Black, Rebecca Black, Rachel Black and Collin Littlesea, and the son of Joseph Black and Jane Clearwater. He also had three sisters named Dorothy, Deborah and Susanah Black.
Sometime during Ephraim Black's life, the Cullen family came to live in Forks near the Quileute reservation of La Push. They were the traditional enemies of the Quileute shape-shifters, and the vampires' presence in the area made those who were of the right age phase into wolves, in preparation of a fight: Ephraim took on the role of Alpha and led the pack. Carlisle Cullen managed to negotiate a peaceful treaty with them: as long as the Cullens didn't bite any humans or cross on to the Quileutes' grounds, the shape-shifters wouldn't attack them or reveal their presence to the humans. Ephraim realized they were outnumbered and there wouldn't have had a need for negotiation unless the Cullens truly meant peace between the clans, therefore he agreed to make the treaty.
They did not encounter any more vampires after the Cullens left, and soon, Ephraim lived out his life as a human.
In Breaking Dawn, the treaty was broken once again with Jacob's permission, to allow Edward to save Bella from death by turning her into a vampire. It's unclear what happened to the treaty after Jacob Black imprinted on Renesmee Cullen, though the relationship between the packs and the Cullens has only grown stronger as a result. The treaty was made exception once again when Alice and Jasper were granted permission to cross on to the Quileute land and run straight into the ocean escorted by the pack leader Sam Uley.
While Ephraim doesn't make an appearance in the book series, he was the Quileute warrior who appeared in the flashback sequence forming the treaty with Carlisle in the Twilight film.
The part was credited only as "Quileute Warrior", however, it is known from the book that the lead Quileute who formed the treaty with the Cullens was, in fact, Ephraim Black. The actor who portrayed the role in the film is Rick Mora.