Originally Posted by
Kaijudo
The first three spots are obviously Luthor, Joker, and Darkseid.
Assuming Fredric Wertham and Dan DiDio aren't eligible, I'm kind of thinking between four characters: Brainiac, Mongul, Despero, and Eclipso. Brainiac is the highest profile, but a lot of his actions boil down to an expanded take upon his programming, which isn't necessarily his fault. He's cold logic while other three seem to be entirely without conscience, something a lot of the other candidates mentioned in this thread have.
Mongul has done a lot of horrible things (Coast City, "For the Man Who Has Everything") but ultimately, from actions to appearance, he comes off as Darkseid Lite. Even Warworld could be consdiered "Your Child's First Apokolips."
Despero is a full-on Justice League villain, versus a single hero's archnemesis. But between his early days as a more calculating villain to his later days as a powerhouse villain, he's been all over the place as far as presentation.
Eclipso, though, is Silver Age possession horror turned into nightmare fuel...he even started out as a villain to himself (via Bruce Gordon). He's an ancient evil god who's killed multiple heroes, is a contemporary of Darkseid, and has evolved into something bigger and badder without entirely losing sight of his earliest appearance. While he hasn't had too much of a media presence, what he has gotten has been used to great effect. He doesn't get used as often as the others but when he is, it's definitely an event.
So yeah, I'm going to say Luthor, Joker, Darkseid, Eclipso.