Over the course of Gotham's run on Fox, one of the most enduring fan theories has suggested that the scheming, yet volatile character Barbara Kean would make a hard departure from her comic book counterpart and eventually become the iconic DC character Harley Quinn. While it ultimately did not come to pass, Gotham showrunner John Stephens confirmed that this twist was, in fact, on the table for the series at one point.
“There was a brief period where we said ‘is there a way to turn her into Harley Quinn?'" Stephens told Fansided. "But we didn’t do that either.”
During this same interview, it was revealed that there were plans for Barbara Kean to have a big "comics canon revelation" at the end of Season 3, alongside the reveal that Butch was actually Solomon Grundy. However, if this had come to pass, it's unclear who she would have actually become.
"I think we were briefly thinking of turning her, for some reason I don’t know why… now it seems like a terrible idea... into Magpie," he admitted. "So we’re not going to do that. We’re just gonna have Magpie."
In late 2016, Erin Richards -- who plays Barbara -- also commented on the possibility of becoming Harley Quinn in an interview with CinemaBlend. However, while she revealed that there had "been discussions," she also stated that she felt a seismic change for Barbara would be necessary to justify her transformation into Harley.
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. It is scheduled to return on Fox for its fifth and final season in 2019.