John Corben (Earth-125)

John Corben was a former member of the United States Armed Forces who became a worldwide hitman and mercenary. After being hired by Lex Luthor to retrieve Kryptonite for LexCorp, Corben became a frequent foe of Superman, and eventually lost most of his body in an attempted homicide against the alien vigilante. He was saved by Lex, who gave him newfound powers through a mechanical body fueled with Kryptonite, thus turning John into Metallo.

Early Life
John Corben joined the United States Marine Corps at age 22, and participated on the Iraq War during the War on Terror. During an engagement against terrorist forces on Iraq, Corben faked his death, wishing to stay away from a "death that he didn't want", and instead chose to become his own soldier.

This led him to turn into a mercenary and bounty hunter through the world, becoming incredibly dangerous and cunning, and using all of his learned Marine training to do so.