John Corben

John Corben was an international assassin-for-hire. He was hired by Lex Luthor to kill his adoptive sister Lena, but in doing so was nearly fatally shot. Corben was subsequently saved by Project Cadmus and modified, becoming known as Metallo. He was eventually killed by Alex Danvers.

Previous jobs
John Corben had links to Intergang, Kasnian terrorists and a genocide that occurred in Corto Maltese.

Attempted assassination of Lena Luthor
Corben was hired by Lex Luthor, who was in maximum security prison, to assassinate his adoptive sister, Lena Luthor. He began by tampering with the oscillator of the Venture space craft, which would be located directly beneath Lena. However, after she couldn't make it due to an important business meeting, subsequently missing the explosion of the craft, Corben had to use an alternate plan to kill her. He took a Heavy Tactical Unmanned Air Vehicle from Baker, using it to target Lena's helicopter, while planting additional drones throughout National City to shoot random civilians; Superman and Supergirl ultimately destroyed all of them, saving Lena. The following day, he planted explosives beneath a plaque at Luthor's ceremony to rename her company. They detonated, along with others planted in the Luthor Corp building. Corben, dressed as a police officer, attempted to approach Lena directly but was intercepted by Alex Danvers. After a brief fight, he took her hostage, threatening to shoot her if Supergirl intervened. He was promptly shot from behind by Lena Luthor, dropping Alex. Sometime later, John found himself connected to medical equipment inside Project Cadmus. A woman approached him, offering to let him live, to which he agreed, and he was injected with something, causing his veins to glow and his eyes to cloud over. The woman dubbed him "Metallo".

Working for Cadmus
After becoming Metallo, Corben initially awoke confused at his newfound strength. When asked who his captor was, the woman responded that she was "merely a Doctor". She introduced him to Cadmus and explained their anti-alien mission, which he hastily sympathized with. He was then dispatched on a mission to kill Supergirl and Superman.

Disguised as a suicidal man on a bridge, he attracted the attention of the Kryptonians who he swiftly defeated, rendering Supergirl unconscious, however he was knocked away by Superman before he could kill her. After converting Gilcrist into Corben's state, Corben drew Superman and Supergirl to his attention while Gilcrist terrorized Metropolis.

Corben later challenged Supergirl, who teamed up with Alex Danvers and removed his Kryptonian heart. Supergirl then spoke through Corben's eyes to Cadmus that she will find them.

Powers

 * Enhanced strength: As a cyborg, John's strength was apparently able to match that of a Kryptonian, however, it should be noted that Superman and Supergirl were weakened by his green energy beam of Kryptonite at the time, in their rematch, Kara who now had an anti-kryptonite suit and at full strength, was able to overpower John easily.
 * Kryptonite beam: John was able to fire a green energy beam of Kryptonite radiation. A sustained blast has shown to cause extreme pain to Supergirl.

Abilities

 * Expert assassin: Working as an assassin-for-hire, Corben was an expert at his profession, having been hired by terrorists and businessman alike.
 * Expert hand-to-hand combatant: Corben had been shown to be able to hold his own in a fight, being able to overpower D.E.O. agent Alex Danvers.