The mysterious Mister X is both the brains and the billions behind the formation of the JLX. This band of mutants broke away from the Judgment League Avengers in order to join him in seeking the lost city of Homo Superior (or mutants), Atlantis. But for Xavier, Atlantis may also hold more beings like himself - Mr X is secretly the Skrullian Manhunter, the last surviving member of the race known as the Skrulls from the planet Mars.
Mister X secretly funded the launch of the Cadmus Project, in the hopes that they would search for the city of Atlantis. Unfortunately for him, the Cadmus Project directed their attention towards the replication of a Super Soldier.