Metallo

Metallo is a name used by multiple supervillains appearing in comic books published by DC Comics, commonly as an adversary of Superman. Metallo is usually depicted as a cyborg with a kryptonite power source in his heart, which he uses as a weapon against Superman. In 2009, Metallo was ranked as IGN's 52nd-greatest comic book villain of all time. Several people at DC have been converted into robots, as depicted in the story. Cyborg, Robotman, and even Cyborg Superman, for example; John Corben, a crook, is one of the most well-known. After a deadly accident mutilates his body beyond repair, Dr. Vale salvages what he can and transplants it into a mechanized body. Vale was scared of Superman and his propensity for destruction, so he created Corben, replete with a Kryptonite power core, to fight the alien.

Vale's orders don't sit well with Metallo, but he inevitably runs with Superman while pursuing his nefarious operations. His life energy is also Superman's death source, which is a lovely irony. He's also changed his appearance on a few occasions, implying that he could appear out of nowhere. He's basically Superman's own Terminator.