Gotham has been bringing a wide variety of legendary DC Comics rogues to the small screen since the first season debuted back in 2014. We've gotten different versions of characters like Penguin and Riddler and Scarecrow than have been presented in other mediums, and the quirks have taught viewers to expect the unexpected. Perhaps the most unexpected character is Jerome, a.k.a. Gotham's proto-Joker. He popped up to wreak havoc on Jim Gordon and Bruce Wayne throughout the first three seasons, and executive producer John Stephens has revealed when we might see him back in Season 4:
What I will say about Jerome is that Jerome is in Arkham right now, and when you think about Arkham's record of keeping people locked up, we will probably see him again before the end of the year.
In true DC Comics fashion, the Gotham version of Arkham Asylum has been pretty terrible at keeping its criminal insane safely away from the citizens of Gotham. Jerome has already broken out, and he proved in Season 3 that even death can't keep him off the streets. Judging by John Stephens' comments at a Gotham roundtable at San Diego Comic-Con, Jerome won't be rotting away in Arkham for too long. He'll probably never be a regular presence on Gotham, but he'll bring the madness for as long as he's around.
Of course, it doesn't sound like we'll be getting Jerome straight away in Season 4, but that's not necessarily a bad thing. There are plenty of stories from the Season 3 finale that still need to be finished. Barbara won't be out of commission indefinitely, despite her electrocution and seeming death in the finale. The Riddler has been frozen in a block of ice to be kept as a prize by Penguin. Butch turned out to be a major villain from Batman lore, and we definitely need some answers about how he's still among the living. Throw in the fact that Scarecrow will be back with a vengeance, and there will undoubtedly be plenty of Gotham action without Jerome spreading his particular brand of madness around the city.
Interestingly, Jerome played a key role in young Bruce Wayne's development into the Dark Knight when they interacted in Season 3. After Jerome kidnapped him and had him tortured and even painted with Joker-esque makeup, Bruce totally snapped and started beating the stuffing out of Jerome, who declared that there are no heroes in Gotham. Bruce stopped himself just short of killing Jerome, which led to the establishment of his #1 rule: he will not kill. When Jerome returns in Season 4, he may have even more of a role to play in Bruce's transformation into the future Caped Crusader.