Millions of years after the destruction of his planet, Xum found the perfect world where his two unborn children would ensure the continuance of his race. Unfortunately, that world was Earth , and the only way to make it a suitable environment was to destroy the ozone layer, which would extinguish all other life on the planet. Shifting from his natural gaseous state into humanoid form, Xum called himself Replikon, and for good reason: besides assuming a hybrid appearance that copied the elements of several members of the JLA, He was also able to duplicate those heroes’ abilities. Replikon also took on a human form and called himself Andre, then proceeded to learn everything he could about Earth from Carol Ferris, the one time love of Green lanterns; Hal Jordan.
Ultimately, Jordan, Green Arrow and Black Canary thwarted Replikon, then returned him to the asteroid belt form where he came. There, he later encountered Green lanterns John Stewart and Katma Tui, who understood the alien’s plight and built him a world within the asteroid belt. Replikon gave birth to Sachi and Yukinori, and the family of three lived happily ever after - that is, until the alien having undergone some alterations, recently returned to Earth, battled Superman in Metropolis, then inexplicably died moments after being defeated. Then Superman faced Xum’s son. Evidence suggests that the Replikons were controlled by an unseen hand, one with particular interest in the Last son of Krypton.
It was later revealed that the villain Ruin (revealed to be Emil Hamilton) was behind Xum’s return, as well as his son’s attack on the Man of Steel .