Krag arrives in a spaceship with markings that point to the planet Mercury. After disembarking, he presents himself as a Mercurian that has learned English by watching the earth with "ultron telescopes and radio receivers". He displays powers equal to Superman and after helping some crooks rob a bank, he claims he is an outlaw that wants to be "King of Crime". To be able to meet the current Crime Czar, he challenges and defeats Superman. Soon after, he is taken to the mob king where Krag unmasks him and takes him to the police.
Superman then reveals Krag was a robot that he controlled by remote control and ventriloquism, and that he often switched costumes and makeup with it (Act No. 165, Feb 1952: "The Man Who Conquered Superman!").