1. A character in digimon adventure, notorious for having an excellent and quite intimidating english voice(Along with some very cool quotes), doing many acts of pure evil(Pumpmon and Gotsumon, anyone), and coming back to life twice. His story arc consists of adventure episodes 22-39, and though he was behind all of 02, he doesn't really play much of a role until near the end.
2. Someone who will not stay dead, no matter how many times you kill them.
As despicable as Naraku may be, I believe there is no one as evil as Vamdemon in any anime, and certainly no one able to be so cool while doing so many acts of great evil.