Harley Quinn is one of the most ubiquitous comic book characters out there—only the thing is, she’s not from a comic book. Created by Paul Dini and Bruce Timm in 1992 for a Batman: The Animated Series episode called “Joker’s Favor,” Harley Quinn was, essentially, a walk-on role, designed and intended to only appear in that one episode and then never to be seen again. As Dini considered the character more, he decided she’d take on more of a Punch and Judy doll-style approach to Joker, that she’d maybe make a joke that Joker’s other henchmen would like, and he’d start to get jealous. The character was a hit amongst the producers and quickly became a staple among Batman’s expansive rogue’s gallery.