It's complicated, but, Klaus is also a werewolf, and because he'd never been triggered, he stayed an Original vampire. There's more, more to it, and his family, but the part that matters here is that, he wanted to trigger the curse. It's what he always wanted. Killing me did that. I'm a doppelgänger. My bloodline was created in order to break the curse. [ Or, this is what she's learned as of now. There's a lot more to it, but to Elena, everything goes back to her. And the Originals. ] There's even more. [ There's always more. ] He's the reason anything has happened to me. Because of him my ancestor killed herself, she became a vampire and ran for over five hundred years. Her name is Katherine and she looks just like me. We're called doppelgängers. [ She was. ]