Asteroid J-54 is an asteroid with a prison facility.
The prison on Asteroid J-54 existed even before Hero Factory came into being.
After Hero Factory began operations, villains such as Voltix and Toxic Reapa who were captured by Alpha 1 Team were sent to J-54. One of Black Phantom's first objectives for the Legion of Darkness was for XT4 to go to J-54 in a stolen Hero Craft to free these two villains. Meanwhile, Splitface and Speeda Demon were sent to hijack an Aird Mining Corporation ore freighter and bring it into orbit around the asteroid. XT4 successfully disabled all of the security robots between the main gate and the two prisoner's cells and played them a recording in which Black Phantom offered them their freedom in exchange for them joining the Legion, to which they readily agreed.
When Preston Stormer, Jimi Stringer, Dunkan Bulk, and Von Ness arrived at the asteroid in two Hero Craft, Stormer instructed Bulk and Von Ness to find XT4 on the surface. Stormer and Stringer tried to open communications with the freighter. However, the two villains set the freighter on a collision course with the Hero Craft and rigged it to explode. Meanwhile, Bulk and Von Ness spotted the villains and tried to prevent their escape, but XT4 used his laser slicer to cut through a security panel and release every villain on J-54. Bulk built a wall of rock around the gate while Von Ness reinforced it with his gravity weapon in order to delay the prisoners' escape. As the prisoners broke through a small portion of the wall, Bulk began throwing them back one at a time.
Von Ness climbed to the roof of the prison, from which he saw the explosion of the ore freighter. Soon afterward, XT4, Voltix, and Toxic Reapa broke through the roof nearby. Recognizing that they outnumbered the Hero, Voltix bargained with him, offering to let him live if he made no mention of encountering the three villains. Von Ness agreed to the bargain, and a few minutes afterward Bulk caught up with his teammate on the roof, having successfully sealed the villains inside the prison. Bulk and Von Ness prepared to pursue the three escaping criminals, but were too late, as the villains took off in the Hero Craft XT4 had stolen. When the two Heroes tried to follow, they found that Toxic Reapa had sabotaged their Hero Craft. Before long, Alpha Team Leader Thresher arrived, recovering the still-intact bodies of Stormer and Stringer from their wrecked Hero Craft and retrieving Bulk and Von Ness from the asteroid's surface.
After the Legion of Darkness was thwarted in their attempt to claim the abandoned Hero Factory as their new headquarters, all the villains involved in the plot were sent to J-54.
Shortly before Mission: Von Nebula, the Villain Storage Unit was built in Hero Factory and all prisoners on J-54 were sent there. After the mass Breakout, it was damaged and the recaptured criminals had to be jailed on J-54 again, though Voltix and Speeda Demon escaped. Black Phantom, Jawblade, Toxic Reapa, Splitface, Thornraxx and XPlode are jailed here and Rocka came to J-54 to question Splitface about Core Hunter, Speeda Demon and the Doom Box map.
Asteroid J-54 is part of a larger belt of asteroids. Being an asteroid, its surface is extremely rocky. The main landmark on J-54 is its prison, which is protected by an automatic security system that fires upon unrecognized spacecraft. The cells of the prison are specialized for countering the unique powers of the villains, and one cell is reserved for use as use as a visitor's area.
Most of J-54's inhabitants are the prisoners detained there, but a number of security robots are also employed to monitor the prison facility.