When they broke into an abandoned military bunker, those blighted survivors of the nuclear war couldn't have realized what they were about to unleash on themselves. Within its derelict walls, they discovered a hibernating computer system. Sensing their movements, the system activated and they found attached to it the head of the Joker suspended in a preservation vessel. The Joker welcomed them with a cackle and told them it was time to build the future.

The Joker told them that the military had wanted to use his unique mind to come up with nuclear war scenarios. Displaying a brutal pragmatism that the Joker appreciated, they put his head in a preservation vessel and got rid of the superfluous parts. Now that the serious world was dead and gone, he told the survivors, it was time to build a new crazy one. So desperate were the survivors that they decided to listen to the Joker and began building a new community within the bunker.

As the community prospered, the survivors increasingly followed the Joker's orders without question, until they eventually had no will of their own. When the Joker commanded that his vessel be attached to the back of one of his minions, so that he could better see the world he was building, many vied for the honor.

The gruesome combat that took place left but one survivor: a scarred, voiceless brute who the Joker named Gaggy. From his spot perched on Gaggy's back, the Joker now rides through the nuclear wasteland, always looking to expand the borders of Jokertown.

The Joker of Earth-17 is the ultimate combination of brains and brawn. His minion Gaggy blindly follows any mad command to come from the Joker, without concern for himself.