Golden Age

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The Golden Age Metalo (different spelling), was a scientist named George Grant. Grant had a powered suit of armor and had taken a serum to increase his strength to super human levels. During their battle, Grant fired a special beam at Superman that dramatically decreased the Man of Steel's power.

Silver Age

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John Corben was once a small-time con man, but that was before a victim of one of his scams rammed his car off the side of a narrow mountain road. Corben's body was crushed, and he would have died within minutes, had the wreck not been found by Professor Emmett Vale. Vale was an eccentric scientist who had spent much of his life scanninig the skies for signs of alien invaders.Vale then told Corben that the kryptonians would invade the planet sohe had to fight Superman.Instead John then snaped val 's neck. Corben now calling himself metallo did fight Superman. Lex Luthor once captured Metallo for his chunk of kryptonite for his own purposes,using a back up power cell Metallo escaped. Metallo then sold his soul to the demon Neron for more power,soon after metallo joined forces with braniac 13.Corben's metallic body grew to giant proportions after absorbing Metroplis technological infrastructure before downgrading to amore human size.Able to shape-shift his body into nearly any mechanical form imaginable,noand desiring nothing other then the death of superman.Metallo not only fought Superman but Batman when the dark knight find out that Corben killed his parents[Thomas and Martha Wayne] in Gotham city