Jonny Frost is a low-level thug who works for The Joker.
Jonny Frost, a low-level thug, is sent to Arkham Asylum to pick up the Joker. Joker immediately takes a liking to Frost, using him as a chauffeur. Frost drives the Joker to the lair of Killer Croc. The three go to the "Grin and Bare It" strip bar, which was formerly owned by the Joker. With the help of Harley Quinn, the Joker kills the new owner and asks the shocked audience if they are willing to help him take his city back. The next morning, the Joker robs a bank and coaxes the Penguin to invest the stolen money. The Joker embarks on a killing spree, murdering many thugs who stole his money, turf, and bizarre sense of reputation. Informed by the Penguin that Harvey Dent, a crime boss with a split personality, is evading a talk with him, an engraged Joker trashes a phone, kills one of his own henchmen, and then sets the "Grin and Bare It" on fire. The next day, Frost is detained by Dent, who warns Frost that the Joker will kill him. Subsequently, Frost is late to the Joker's meeting with the Riddler, a disabled weapons dealer. They exchange a briefcase, and the Joker leaves. Once on the road, the Joker's crew is shot at by off-duty cops hired by Dent, and Frost saves the Joker's life in the scuffle.
Joker embarks on a turf war against Dent, prompting him to meet with Joker. They meet at the city zoo. Joker brings the briefcase he got from the Riddler. Joker says he has learned Dent has two wives, and threatens to use the contents of the briefcase as leverage against him. The meeting becomes hostile. Joker attacks Dent, with shards of broken glass glued to his fingertips. When Dent's men raise their guns, Harley shoots each one in the head. After helping Frost get his ex-wife Shelly back from Dent, Joker rapes her. He says this makes them even, since Frost "cheated" on the Joker by not revealing his own meeting with Dent. Later, Harvey paints a bat on a spotlight, and pleads with Batman to stop Joker. When Joker and Frost return to their apartment, they find the window shattered and flee to Croc's lair. However, Batman has already subdued Croc and his gang. In a final attempt to escape, Joker and Frost flee to a nearby bridge. While Joker is "screaming through tears", Jonny inexplicably finds himself laughing, unable to stop. They find Batman in wait, and Joker, being provoked by Batman's tauntings, shoots Frost in the chin. Joker and Batman fight as Frost climbs over the edge of the bridge and falls.
Jonny Frost appears in the 2016 film Suicide Squad, where he is portrayed by American actor Jim Parrack. In the film, he serves as the right hand man of Joker.