At a later point, Tess Mercer received an update on Corben, who had apparently been "repaired". However, the operations have left him more machine than man, also leaving no vital signs. Later, when Tess visited Winslow Schott, a mad criminal genius who used to work for Lex, she gave him John's kryptonite heart for him to tinker with in an attempt to see if he could help reboot John's systems.
Later, when it was revealed that Kandorians were experimenting on humans, Clark asked a doctor if there was any of the humans that were experimented on and never found. The only one was John Corben. Later, it was revealed that Tess' scientists were able to correct the adrenal flaw in the Kryptonite matrix, thereby returning Corben to sanity. Seeing him as a potential weapon if the Kryptonians ever turned hostile, they implanted a control chip into the back of his neck that would turn him in to a mindless drone. Lois infiltrated the base where experiments were being done on red kryptonite just as they were bringing Corben back online. When she was discovered, the scuffle set of an explosion from the red kryptonite, throwing her through the base and down an elevator shaft, only to be caught by the reactivated Corben. Waking up the next morning not remembering how she got home, Lois later found him in the Talon basement. While understandably skeptical after their last encounter, Corben assured her he was now sane and he had saved her the previous night. He explained to her about Tess' experiments and the control chip but also that his artificial heart was nearly out of energy and unless he replenished it soon with more meteor rock, it would deactivate and effectively kill him. Taking him to one of Chloe's weapon stashes, Corben was able to recharge the Kryptonite matrix with liquid meteor rock. He then encountered Clark (who was under the influence of red kryptonite) but before anything could happen, Zod blew the truck up with his heat vision. He survived and Lois found him nearby unharmed, having been blown from the wreckage.
Deciding it was best to get him somewhere safe, Lois was prepared to take him over to the Badlands and out of Tess' reach to a doctor she trusted. Before they could get on the bus, one of Tess' people slipped the control chip onto the port of his neck, instantly taking over his mind. He then returned to the lab, where Tess and Chloe prepared him to stop the Red K infected Clark, who had taken Zod to the Fortress. Chloe, still not trusting Tess deactivated the monitoring system so Tess wouldn't learn the location of the Fortress. Arriving at the Fortress, he was confronted by Zod and Clark. While he had the advantage due to the Kryptonite Matrix, his lack of free will made it difficult for him to effectively battle the two when they split up. The control chip was knocked loose by debris and his mind restored when Clark used his heat vision to bring down part of the Fortress roof on the cyborg intending to crush him.
Coming back to his senses Corben, went straight for Clark again only to be frozen solid by a combination of his and Zod's super breath. This was short lived when they noticed the Matrix began to beat at a faster rate and Corben proceeded to smash his way out of the ice with ease. Being so close to him, they were helpless against the aura of the kryptonite matrix and Corben proceeded to kick Zod into one of the fortress walls. Turning his attention back to Clark, he pulled out a krytonite shard he had been given by Chloe, saying he didn't blame Clark for attacking him in the past but someone who cared about Clark sent him to help. Grinning madly, Clark said he didn't need saving, as Corben knelt down next to him saying from experience that sometimes people don't know when they need saving before stabbing Clark with the shard, freeing him from the Red K. Now back in the right state of mind, Clark lept backwards carefully, observing the cyborg. Corben picked up the removed control chip so no one could control him again and waved off Clark's suspicion of him by saying Clark could thank him another time. He pulled out the Key to the Fortress and placed it in the console, disappearing in a flash of light. After that, John met Lois on the streets of Metropolis. She gave him a new Kryptonite heart, this one being powered by Red Kryptonite instead of green. Corben said that he was going to go underground and wanted Lois to come with him. Lois told him that there was someone else in her life (Clark) and that he was the one. After saying their goodbyes, Corben left. John, now going under the name 'Metallo', was a part of the Toyman's Marionette Ventures league of villains. During their meeting, each member was assigned a target from the Justice League. Metallo's target was Supergirl.
