1. Joker
Batman is the most popular superhero in the world because he has the best rogues' gallery out of anyone in comics, and Joker is easily the best of the bunch. An insane, homicidal clown fighting a billionaire dressed as a bat - as setups go, they don't get more memorable than that. Created by Jerry Robinson, Bill Finger and Bob Kane in 1940, Robinson based the character's look on Conrad Veidt's character in The Man Who Laughs (the title of which would later become a brilliant Batman book by Ed Brubaker) - seriously, google that actor's name with that movie title and tell me that isn't the devil himself. Combine Veidt's horrifying look with a clown and you've got an immortal character. Joker might be the only person Batman is afraid of, because he doesn't understand him and can never understand him. The character's past is unknown, though some writers have attempted to write it. Most memorably is Alan Moore's portrayal in The Killing Joke where Joker is depicted as a failed comedian in need of money for his wife and kid who falls in with a gang that winds up at ACE Chemicals. The poor guy falls into one of the vats and the chemicals gave him the white skin, green hair, and permanent smile, while also shattering his mind. Joker's unknown past has served the character well in the cinematic masterpiece, The Dark Knight, where Heath Ledger spins numerous versions of how he got the scars that make up his grotesque smile, while Batman desperately tries to find out who the man is and why he's doing what he's doing, with no success. Jack Nicholson's portrayal took the ACE Chemicals storyline but meshed it with a gangster angle in another successful version of the character in 1989's Batman, while Mark Hamill has done amazing voice-over work as the Joker in the Arkham Asylum games and Batman: The Animated Series. Meanwhile in the comics, Joker's responsible for some of the biggest events in Batman's life - as any great nemesis should be. He murdered the second Robin, Jason Todd, and crippled Commissioner Gordon's (Batman's best friend) daughter Barbara, putting her in a wheelchair until recently when the character was rebooted and given back the ability to walk. DC took the bold step of removing Joker from the entire first year of their line-wide reboot, the New 52, after just one appearance in Detective Comics where he escaped Arkham, gruesomely removing his face in the process. While the face removal was quite bizarre, Joker's return in 2012 was heralded by the brilliant storyline, Death of the Family, as Joker set about dismantling Bruce's cadre of fellow Bat-vigilantes. The purple suit, green hair, white face, red lips, and manic laughter all give Joker an iconic look that's rarely changed in the 70+ years the character has been around, proof positive of its effectiveness. Meanwhile, DC has wisely steered clear of giving Joker much backstory, instead choosing to focus on what he's planning in the future, making him permanently mysterious and unknowable - fodder which keeps us all reading. Part of the brilliance of the character is that he's human, like Batman. He's no god, has no superpowers, he's just a criminal mastermind - the clown prince of crime! - who may or may not be crazy. He must be crazy given his actions and behaviour but then could a truly crazy person concoct such elaborate schemes and plans that confound the world's greatest detective, Batman? Plus Joker has gotten the upper hand to Batman several times and had a number of successful plans executed, all of which would require a degree of mental clarity - could it all be an act? If he is completely sane, it would also make him completely evil, which is quite possible. There are a number of excellent Joker books that are worth checking out - the aforementioned Death of the Family is the greatest latest one, but others include The Killing Joke, The Man Who Laughs, Mad Love, Arkham Asylum and Brian Azzarello's Joker. That's the list - did I miss out your favourite super-villain? Let me know in the comments below!