Harley Quinn has grown into one of the most identifiable members of the DC Universe. Created for Batman: The Animated Series, the sidekick and lover to the Joker has morphed from henchwoman and dark paramour into a compelling, and beloved, character in her own right.

After years of teasing the arrival of the Clown Prince of Crime, Fox's Gotham is poised to let him loose for the fifth and final season. Actor Cameron Monaghan, who plays both Jeremiah Valeska and his late twin Jerome on the Batman prequel, has hinted on social media that he won’t be alone in his mayhem, posting photos of his proto-Joker with a young woman who looks a lot like Harley.

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It’s been a long time coming, with the cast and crew of Gotham waffling over which character might become Harley, or whether the fan-favorite antiheroine would ever appear at all.

Misdirection Is the Key to Comedy

Harley has been teased since at least Season 3, with executive producer John Stephens hinting that she (and Killer Croc) would appear before long. “The Harley Quinn of it all is a bit more of a sticky wicket, but it's one we've already thought about for the character," he said in January 2017. "We don't want to give too much away but it will definitely be someone connected to the Joker cult world that we have set up. But it's down the road, later in Season 3 right now."

Although a minor character believed to be Killer Croc was spotted among the villains unleashed from the Indian Hill experiments, there wasn’t any impression that Harley had shown her true colors.

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Even star David Mazouz, who plays young Bruce Wayne, suggested that Harley Quinn would appear in the Season 3 finale. However, when there was no big reveal in that episode, fans began to wonder if one of the established cast would turn out to be the Gotham's incarnation of Harley.

Executive producer Ken Woodruff went so far as to suggest before the Season 3 premiere that, “You may have already seen Harley as a person that you thought you had met and known for a long time." Some fans speculated that Harley could be someone like Selina Kyle or Leslie Thompkins in a major plot twist. But the longest-running theory centered on Barbara Kean.

Barbara Kean

During the third and fourth seasons, many Gotham fans gravitated toward the idea that Harley Quinn had been hidden in plain sight from the very beginning. But instead of being a psychiatrist named Harleen Quinzel, she would turn out to be Barbara Kean, ex-fiancée of Jim Gordon who went off the deep end after murdering her parents.

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Barbara became a major figure in Gotham's criminal underworld, even working alongside Jerome on occasion. That change to her character led some viewers to theorize she was on her way to becoming Harley. The show's producers even seemed to tease that genesis with costume choices for Barbara evocative of Harley Quinn’s classic look.

When asked about that possibility, executive producer Danny Cannon refused to confirm or deny what would become of Barbara going into the fourth season. In the end, however, Barbara wasn’t Harley. Instead of teaming with the Joker, she joined another major Batman villain, Ra’s al Ghul. She even became the Demon’s Head.

In later interviews, Stephens revealed they did consider transforming Barbara into Harley Quinn, but ultimately decided against it. He also revealed producers had toyed with turning her into the far lesser-known DC villain Magpie before abandoning that idea as well.

One Last Misdirect

Come Season 4, Stephens insisted that Harley wouldn't appear on Gotham at all. Although the producers transferred some of Harley's chaotic energy to Barbara, he said, "It’s not going to happen… Let’s put it out there. The discussions we’ve been having is – Look, we know Harley Quinn is never going to be on our show."

But then, at the end of the season, audiences were given a new contender for the role: Ecco, the personal assistant/bodyguard for Jeremiah Valeska. Devoted to her employer, Ecco followed Jeremiah even as embraced his madness. The character took on a new look, one familiar to DC fans.

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Although the colors were muted and the costume added a full mask, the costume was clearly intended to evoke the classic Harley design. Working alongside Jeremiah, the pair is the closest the series has ever come to a Joker/Harley team-up.

Stephens hinted more at the character last month at New York Comic Con, saying “[Jeremiah] has a somewhat-deranged girlfriend who dresses in a multi-colored fashion. I wouldn't describe it as a healthy relationship, but there's a meeting of minds …” That sounds about right for Harley.

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Monaghan posted photos of his Joker hand in hand with a blonde woman who looks strikingly like a wild Ecco. With the two going off the rails during "No Man’s Land," and the end of the series rapidly approaching, it seems like we’re finally going to get the Gotham Harley Quinn we’ve been waiting for. That is, unless producers fool us again.

Returning Thursday, Jan. 3, on Fox, Gotham stars Ben McKenzie as James Gordon, Donal Logue as Harvey Bullock, David Mazouz as Bruce Wayne, Robin Lord Taylor as Penguin, Camren Bicondova as Selina Kyle, Erin Richards as Barbara Kean and Sean Pertwee as Alfred Pennyworth.