Cain Marko was the stepbrother of Professor X. In an ancient cave he discovered a large gem that turned him into a human juggernaut, but he was presumed dead when the cave collapsed.

Years later he attacked the X-Mansion, wearing a helmet to block his stepbrother's telepathy, but Charles recognized him anyway. As Juggernaut, he then became a member of Magneto's Brotherhood of Evil Mutants, despite not actually being a mutant.