The history of the individual whose brain became the Robot Criminal is largely unknown.  It is known that in 1949 he was sentence to death in the electric chair for unidentified crimes but escaped at the last minute, stealing a plane to elude the police.  Whether through his own actions or those of the police, the plane was downed and the criminal pilot was killed in the process.  He did not sustain significant head trauma and his brain was intact, a fact that determined later events.

During that year, and for some undetermined period before, the roboticist and physician Dr. Manfred Zanger had been studying Robotman with the intention of duplicating the experiment that had given the hero life.  He had created a similar, possibly more advanced robot body but lacked a subject on which to test it.  Contacted by unknown parties, Zanger secured a human brain, unknown to him that of the criminal who had been killed the downed plane.  Through a mutual friend, Zanger invited Paul Dennis (secretly Robotman) to observe the process and initially, Dennis was elated that he might have a friend and ally who could relate to his life as a human robot.

Zanger's surgery was a success and the new robotic being gained consciousness.  Quickly grasping his new circumstances, the subject revealed his criminal nature and broke through a wall to avenge himself on those who had killed him.   After changing from his Paul Dennis identity, Robotman followed a trail of destruction to the police station where he found the Robot Criminal thrashing the police.  Seeing his nemesis arriving, the Criminal turned his attention on Robotman,

The two robotic beings engaged in direct combat with Robotman struggling to gain the upper hand.  Zanger had evidently created a body that was larger, heavier and stronger than Robotman and the Criminal used that to full advantage.  Realizing direct combat would not succeed, Robotman races to the riverfront, calculating that the new-to-robot-life Criminal would have not have mastered swimming in his new robotic form.  While that was proven true, Robotman discovered that Zanger had given his robot body the ability to survive underwater and the Criminal simply walked out of the river.

Becoming somewhat desperate, Robotman taunted the criminal from an elevated subway train platform. Taking the bait, the Robot Criminal climbed the scaffolding and Robotman "warned" him that third rail was electrified, even tho he himself was standing on it.  The Criminal scoffed that Robotman was attempted to deceive him but in reality, Robotman had coated his feeding an insulating plastic so the Criminal touched the rail, he was electrocuted and presumably killed.  Zanger, feeling defeated, abandoned any effort to reproduce Robotman again (Detective Comics #153).

What became of the Robot Criminal's body and whether Zanger maintained his refusal to do further research are unknown.