Cain

Cain was the vampire responsible for turning Tatsuhiko Shido into a vampire, as well as erasing his past memories. A handsome, hedonistic, yet cruel individual, Cain has pursued Shido for the past few hundred years.

Cain and Shido were at one time lovers, but because of Cain's cruelty, Shido broke away from him and began his quest against nightbreeds. Cain, however, refuses to let Shido go, and is hoping for the day that he and Shido would be together again.

(source: Absolute Anime)