Red Skull! Anyone who is too crazy/evil/murderous for Hitler is a bad, bad person. And AWESOME.
Red Skull! Anyone who is too crazy/evil/murderous for Hitler is a bad, bad person. And AWESOME.
As others have said:
Doom
Thanos
Kang
Red Skull
I'd also add Loki and Mandarin, both are great.
And finally, Magneto- enough with the reformation already, make him a villain again. He's so much better as a villain who has a point than as a reformed former villain. They have plenty of characters like that.