My choice is Unicron. Galvatron is just an upgraded version of Megs and er, being insane is an excuse! LOL!
Unicron, master of chaos, destroyer of worlds. He's the personification of evil and the perfect killing machine, unremorseful and uncaring. A close second is any casting director who has ever uttered the words, "You know who would be great in this part? Steven Seagal."