I'm fond of Vecna.
I love him.
1. He was one of the most ancient (if not the most ancient) archvillain of D&D
2. He's the main character of three great adventures (Vecna Lives!, Vecna Reborn, Die Vecna Die!)
3. He was taught magic from an evil god
4. He was a so powerful archwizard (and archlich) who had become a god himself by his own powers
5. He had cheated Iuz and can still boasts about it
6. He was the only one who was trapped in Ravenloft demiplane and still managed to escape
7. He was the only god to enter in Sigil
8. He had lost limbs which had become powerful artifacts themselves
9. He was betrayed by his most trusted lieutnant and he had learned to never trust anyone again
10. Through his actions the second edition ended and the third began, and the D&D game had never been the same