Ground Zero was once Dr. Milton Chaba, a genius physicist who worked for U.S.H.E.R. R&D designing a new generation of radiation treatments. During one of these experiments, Chaba was consumed in an explosion and transformed into a creature of pure radiation. He emits lethal doses constantly, killing anyone who comes into contact with him. Worse, every few hours the energy builds up and he must release it in an explosion killing anyone nearby.
After accidentally killing the saboteurs that caused the explosion Milton fled into the Arizona desert, where his only contact was with Atrocity, a creature who seemed both immune to his powers and strangely calm in his presence. During the Scion invasion, when it seemed all might be lost, Ground Zero came out of the desert and stood with Earth’s heroes to defeat the mad galactic emperor.
After receiving a promise that he would never be used as a weapon, Ground Zero turned himself over to U.S.H.E.R. agents for voluntary incarceration in Rock City. There he renewed his strange friendship with Atrocity, during brief periods when the creature is wakened, Ground Zero is always present to keep it calm. To date requests by U.S.H.E.R. scientists that Atrocity be awakened permanently in the hopes that Ground Zero would be able to return the creature to a semblance of sanity have been rejected as too dangerous.