Thanks in large part to the vocal performance of Arleen Sorkin — a friend of Dini's and, according to interviews, a model for how he envisioned the character — Harley quickly became a favorite both of viewers and those working on the series, returning a number of times both in and out of the company of the Joker. In fact, the character became so popular that she was the subject of Mad Love, a 1994 spinoff graphic novel set in the animated series' continuity by Dini and the show's art director Bruce Timm that revealed her origin story.

Mad Love didn't just introduce the backstory of Harley — a former psychiatrist called Harleen Quinzel, she fell in love with the Joker while interning at Arkham Asylum and freed him in an attempt to win his heart — it also showed how easily the character could support the weight of a story by herself when given the chance. It's unlikely to be a coincidence that she starred in her first animated episode without the Joker (Season 2's "Harley's Holiday") soon after the release of the book.

As a result of her increasing popularity in the animated world, Harley crossed over into the "regular" DC comic book universe in a 1999 graphic novel titled, appropriately, Batman: Harley Quinn, before receiving her first solo monthly series in 2001, which saw the character leave Gotham City for Metropolis and a new life. After 38 issues — and plots that included Quinn's death and subsequent rebirth, because comics — the title was canceled in 2003, with Quinn reduced to making occasional guest appearances in Batman and related comic book series for the next few years, with the exception of a team-up with fellow villain Poison Ivy in 2004's three-issue Batman: Harley and Ivy mini-series.

The partnership between the two villains would also be at the heart of Harley's next starring role, with creator Dini returning to the character to write the Gotham City Sirens series that ran from 2009 through 2011 and featured Harley, Ivy and Catwoman as lead characters. Following DC's line-wide "New 52" reboot in September 2011, Harley was placed in the revival of the Suicide Squad series, where she remains to this day, inspiring the upcoming movie incarnation of the character.

That, however, isn't the end of Harley's story. Indeed, it arguably misses the most interesting part of the character's comic book history. In 2013, DC launched a second solo Harley Quinn comic book, written by Amanda Conner and Jimmy Palmiotti, with art by Chad Hardin and John Timms. Ostensibly taking place in the same world as Suicide Squad, this Harley offers a very different take on the character, one that's more fun and irreverent towards not only Harley herself, but also the superhero universe she inhabits.

Tellingly, it's also a series that's found significant sales success — outselling Superman, Justice League and Green Lantern titles, as well as the majority of the remainder of DC's line — while allowing Harley to evolve as an individual; this version of the character has acknowledged the abusive nature of her relationship to the Joker and attempted to move on, with Conner and Palmiotti admitting publicly that fans' subtextual reading of her friendship with Poison Ivy actually being a romantic relationship is, in fact, their own intention in writing the two together.

Whether audiences are responding to the growth in the character, or simply to the silliness and fun the series offers — amongst other problems, Harley has had to deal with Captain Horatio Strong, a Popeye parody who gained superhuman strength from an addictive alien plant that he believed was spinach — the success of the series has pushed Harley to the forefront of DC's publishing plans. In addition to the monthly Harley Quinn series, Conner and Palmiotti have written a number of special issues, spin-off mini-series and an ongoing team-up title (Harley's Little Black Book) featuring the character, with little sign that her popularity has peaked just yet.

It's in this space where Margot Robbie enters the picture, playing a genuine rarity in modern superhero mythology: a character created in the last two decades who has become an accepted comic book icon, a fan-favorite anti-hero who is looked up to as a representative for under-represented demographics, and someone who purposefully embraces their outsider status and rejects the status quo.

In truth, there's really only one other character who can claim a similar position: Marvel's Deadpool. And we all know what happened when he finally reached the big screen, don't we…?

Suicide Squad opens Aug. 5.