Cordelia Spears is the first Vampire ever. She was born a Vampire, actually, never wanting to be one at all. When she, and her coven moves to the boundaries of Port Angeles and Forks, she isn't wanted by the Coven close by, the Cullens, and the werewolves, but she's not going anywhere. Nobody speaks of her, but they know her reputation of having no heart when it comes to killing anyone. Even the Volturi are afraid.
What happens when she warns Edward Cullen, and he takes it as a threat. Time will tell.