thought of some others
King Hamdo from Now and Then Here and There
One of the best villians ever, everything about him is perfect. I'll give you a taste of what he's like, he strangles cats to death to vent his frustration. Also, his english voice actor conveys his madness fantastically.
Kamineko from Azumanga Daioh
A cat who delights in taunting (and biting) Sakaki, a harmless girl whose one wish is to pet him. Make no mistake about it, if Kamineko was a person he'd be one evil bastard.
Legato from Trigun
He believes humanity is vile and should be exterminated. But that's not what puts him on the map, that would be his last action in the show. Hmm, can't say anything without spoiling it and trust me, you don't want this scene spoiled for you.
