Harley Quinn Appearances
Harley is a comic book character originally created in the Batman Animated Series by visionary series creators Bruce Tim & Paul Dini, who based her heavily on Arleen Sorkin, the actress that voiced her. She's become one of the highest profile characters in comics regardless of gender, which is huge.
In the comics, Harley is now a mainstay of the Suicide Squad, as well as the star of several ongoing solo series. She's appeared in dozens of animated projects where she's been voiced by Laura Bailey, Tara Strong, Jenny Slate, Melissa Rauch & Kaley Cuoco, among others.
During the short-lived 2002 series Birds of Prey a very different, more calculating Harley was the series villain. She was played by Ferris Bueller allum, Mia Sara.
A list of live-action Harley Quinn's has to include the character Ecco played by Francesca Root-Dodson on the series Gotham. The series played very loosely with Batman continuity, and this character was never meant to actually be Harley herself, but she used so many of the character's manerisms she was clearly at least an homage.
Of course, the ACTUAL live-action Harley Quinn is Margot Robbie. She was one of the best parts of the 2016 Suicide Squad movie, where Robbie managed to actually depict the character's open defiance of her own abuse in a movie that seemed determined NOT to. She then went on to become the producer on the Harley-led movie Birds of Prey, which turned out to be intensely awesome. Harley Quinn, in all her brokenness, has managed to lift herself up and become a femminist icon all on her own, and Robbie gets a lot of credit for that.