The people now known as the Daxamites were originally Kryptonians who left their homeworld to explore the universe (in post-"Crisis on Infinite Earths" continuity, the Eradicator, an artificial lifeform programmed to preserve all Kryptonian culture, altered the birthing matrices ("artificial wombs") that the explorers took with them so that all newborns would be fatally vulnerable to lead and other materials such as greenhouse gases and certain rocks). Thus, if they persisted in their anti-Kryptonian wanderlust, they would all die from it. One Daxamite, Mon-El, was poisoned by lead and preserved in the Phantom Zone until a cure was found by Brainiac 5 in the 30th century, whereafter Mon-El became a member of the Legion of Super-Heroes.