Beginning life as The Joker's marginally less psychopathic girlfriend/side-kick, at this point Harley Quinn might even been verging on a similar level of popularity to the Clown Prince Of Crime: her solo comic book series is a huge seller for DC, she's reached new of fans thanks to her appearances in the Arkham series of Batman video games, and she's got a starring role in the upcoming Suicide Squad film, played by Margot Robbie. Before The Wolf Of Wall Street got her teeth into her, Harley Quinn was just the simple, if somewhat troubled, psychiatrist Dr Harleen Quinzel (how did she not know she was destined for supervillainy with a name like that?). It remains to be seen if Suicide Squad follows the same pattern, but almost every version of Harley's origin up until now has her assigned to be The Joker's therapist, only to fall in love with him and his madness. You can see why the character appeals so much dudes like her costume to gawp at, girls like her costume to cosplay in, readers love her as the lighter side of The Joker who it's usually okay to laugh along with, and who you can actually sympathise with. And if the leaked Suicide Squad premise is to be believed, The Joker is more of a secondary character; Robbie's Harley takes centre stage. It's safe to say that all lights are on the former Dr Quinzel right now, but what is there about the character that Suicide Squad won't tell you? What's the mysterious past that doesn't get explored in her wacky comic? From alternate worlds to previous live-action appearances, secret origins to surprising character arcs, here are ten things you didn't know about Harley Quinn.