Nahuel, the Key Witness
Nahuel arrives with Alice and Jasper in the deciding moment of confrontation between the Volturi and the Cullens. A human-vampire hybrid, like Renesmee, he was created by a vampire named Joham and a human woman named Pire. His mother died during childbirth. Nahuel's story proves to the Volturi that vampire hybrids like Renesmee don't pose any threat to them, which forces them to retreat.