When it comes to comic books the most famous characters are mostly heroes obviously but who are the villains who even non comic book fans could recognize? I think the list would include:
The Joker (clearly the most popular villain in all of comic books)
Lex Luthor (I'd say he's not quite as famous as Joker but very close after all he is Superman's number 1 villain)
Others: The Penguin, Riddler, Dr. Doom, Doc Ock, Green Goblin.