Strips 6243-6338 (December 15, 1958 to April 4, 1959)
Professor Vale rescues a man from an accident, but the only way to save his life is to perform a desperate experiment of transplanting a mechanical heart into his body. However, upon waking, the patient becomes furious with his mechanical body. The professor explains the situation to him, and that his body is powered by expensive uranium pellets. When he escapes though, will Superman be able to stop him?
Notes: This is the first appearance of the character Metallo. He does not appear in the comics until later. This story was retold in Action Comics #252 (May 1959).
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