Rex served as Apocalypse's servent and errand boy. It is uncertain whether or not Rex is a mutant because Apocalypse referred to him as being both a flatscan and a lowly mutate. If he is a mutant, it is surmised that he had a relatively weak mutation. When Delgado was able to infiltrate the X-Men's base of operations, Rex informed Apocalypse of Delgado's breech through Blink's portal and once again reported in when they pinpointed the location to be in Westchester. Before Apocalypse departed to attack the X-Men's headquarters, Rex began an interrogation with Sebastian Shaw on the mutant Karma. Before Apocalypse's left for his offensive, he learned of Sinister's betrayal and sent Rex with instructions for the immediate shut down of the Pens.

During the last stand at Apocalypse's Citadel, Rex was seen checking to make sure that the trap set for the X-Men was intact and in place. He was last spotted after reporting that the entire Midwest was a radioactive crater as a result of the Human High Council's pre-emptive nuclear strike that started from within the United States! In order to retaliate, Apocalypse sent Rex to expand the Sea Wall Defense Grid across the Atlantic, attacking the human populated Eurasia. It is unknown what become of him after the fall of Apocalypse.