As Mongul delivered the killing blow, Superman vanished. At first it was thought that the tyrant had killed him, but this was not the case. Superman had been transported to a nearby asteroid, where he met an ancient cleric who claimed to have been on Krypton during the planet's fifth historical age, thousands of years before its destruction. The Cleric had a gift for Superman--an ancient Kryptonian relic called the Eradicator which the Cleric gave to Superman, claiming that the device was his birthright. This made some sense, given that the Eradicator had been designed by Kem-L, an ancestor of Superman's family line, the House of El.

The Eradicator fixed Superman's costume, which had been destroyed, and transported him back to Earth. But after doing those two favors, the device from Krypton's past seemed determined to destroy Superman's life on Earth.

The Eradicator jeopardized the lives of many close to Superman, particularly young Jimmy Olsen. Realizing that the Kryptonian artifact posed such a danger, Superman tried to dispose of it in a deep crevasse at the South Pole. But the device would not be contained, and immediately began construction of a Kryptonian fortress at the site, as part of a larger plan to turn the Earth into another Krypton. Superman battled with the device, trying to force it to shut down. In desperation, Superman opened his mind to the Eradicator, willing it to recognize and accept him as its master, a member of the House of El.

This seemed to work for a time. The Eradicator ceased its attempt to bring Krypton to life on Earth, and Superman returned to his life as Clark Kent. However, as time went on, Clark's friends began noticing a strange change coming over him. He became cold, withdrawn, and aloof. In fact, his mind was changing to more closely reflect the logic-driven, emotionless mind-set of Krypton's last residents. In keeping with that, Kal-El abandoned both his identity as Clark Kent and his role as Superman, and took up residence in his Kryptonian Fortress.

He might have stayed there forever, had Jonathan and Martha Kent not been able to break him out of his hypnosis. When he realized how the Eradicator had been controlling his mind, turning him into a cold, emotionless Kryptonian, he destroyed the Fortress and threw the Eradicator into the sun. Then, he returned to his life as Clark Kent.

Speaking of Clark Kent...