The armor built on Apokalips for Superman during the Our Worlds At War storyline. Darksied originally intended it to be used by Superman to defeat Imperiex, but Superman sensed that the despot was up to no good and refused to don the suit. The armor was built out of the armor of a destroyed Imperiex probe, and would have given the wearer a fighting chance against other Imperiex probes.
Later the suit was given to a revived John Henry Irons (Steel). It proved to be pivotal in the plan to destroy B13 and Warworld by acting as a crucible to mix Brainiac 13 technology and Apokaliptian technology to bend time and space.
Superman was right to decline Darksied's offer, as it later came to be known that the wearer started developing a dependency to the armor. When John Henry could no longer use his Steel armor because of the damage caused to his nervous system, he was forced to wear the Aegis armor or "Entropy Aegis" armor, and was called back to Apokalips.
In the end Superman fought Darkseid for John Henry and brought John Henry Irons back to earth. The Entropy Aegis Armor was shown to hold the powers of entropy and Darksied had wanted the wearer to incubate a being that would contain the soul of a creature that would wield the power of ultimate destruction. Of course, Superman and the other existing kryptonians (Superdog, Superboy, Supergirl, the Eradicator, and another Supergirl) along with Natasha Irons, thwarted Darksied's plans on his homeworld, Apokalips.