Birds of Prey (And The Fantabulous Emancipation of One Harley Quinn) includes an Easter egg that hints at the true origins of the Harley Quinn character. Created in 1992 for Batman: The Animated Series by Paul Dini and Bruce Timm, Harley Quinn has become a staple of Batman’s rogue’s gallery, appearing in cartoons, comics, video games, and now feature films.

In Birds of Prey, Margot Robbie plays Harley Quinn, reprising the role she first portrayed in 2016’s Suicide Squad. That film depicts Harley’s origin in more or less the same manner as the animated series: Dr. Harleen Quinzel is an Arkham Asylum psychiatrist who falls madly in love with the Joker, helping him to escape and joining him as his partner in actual crime, the newly christened Harley Quinn. Suicide Squad would also include the more modern addition to Harley’s origin - a quick dip in a vat of acid that bleaches her skin the same stark white as the Joker’s - only in the film, she chooses to jump instead of being pushed in. Birds of Prey briefly recaps and even adds to Harley’s origin story at the very start of the movie, but it also makes sure to include a nod to the character’s real origin.

As mentioned above, Harley Quinn was created by writer Dini and artist Timm while both were working on Batman: The Animated Series. At the time, there was talk of giving the Joker a new sidekick character in an upcoming episode and Dini was considering a kind of henchwoman. Around that same time, Dini’s college friend, actress Arleen Sorkin, was appearing on the soap opera, Days of Our Lives, and a recent a string of episodes had her character appearing in a harlequin costume during its strange dream sequences. Sorkin taped the episodes and shared them with Dini, who upon seeing Sorkin in the harlequin makeup and costume, became inspired, and after consulting with Timm on the design, their Harley Quinn was born. In Birds of Prey, a clip of Sorkin dressed as the harlequin from Days of Our Lives can be seen playing on the television in Renee Montoya’s apartment as a callback to where it all really began for Harley.

In addition to serving as the visual inspiration for Harley Quinn, Dini claims to have modeled some of Harley’s personality and mannerisms on Sorkin as well. So when it came time to cast for the role, there was really no other option but Sorkin, whose vocal performance (and in particular her East Coast accent) have since become synonymous with the character. Originally planned to only appear in one episode (season 1’s “Joker’s Favor”), Harley proved so popular that she returned again and again throughout Batman: The Animated Series as well as its many follow-up series and animated films.

Sorkin’s last time performing Harley Quinn’s voice came in two video games, 2009’s Batman: Arkham Asylum and 2011’s DC Universe Online, reuniting her with her Batman: The Animated Series co-stars Kevin Conroy and Mark Hamill. By now, Harley Quinn is a bona fide star and the character has since been voiced by several actresses, including Tara Strong (Teen Titans, My Little Pony) and most recently The Big Bang Theory’s Kaley Cuoco in Harley’s very own animated series on DC Universe.

On the big screen, of course, it’s Robbie who embodies Harley Quinn, and in Birds of Prey, she fully embraces Harley’s fun-loving, chaotic attitude. She builds on what has come before, though, and that’s largely indebted to not only Sorkin’s performance but the unlikely inspiration that came from her time as a soap opera harlequin.

More: How Birds Of Prey Sets Up A Proper Harley Quinn Sequel

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