Villain type: Predator by necessity. This includes supernatural predators such as vampires, or starving-assassin type figures. They could have been good people... but they "had no choice" but to do bad things. The tragic hero fights it. The villainous predator by necessity embraces it, using a physical need or compulsion as an excuse. Conversely, you could make them fight the need, but still succumb to it as a tragic villain.