The original Zilla resurrected by alien and human technology. He is completely controlled by the Tachyons, though he does recognise Zilla jr. as his son.
The original Zilla resurrected as a cyborg by the Tachyons, he was first sent out to kill Nick Tatopoulos and Dr. Mendel Craven who were spying on the Tachyons. However Zilla Jr. came came to defend them but instead got confused at seeing another Zilla which allowed the Tachyons to control him. He then traveled to Site Omega with his son before he was sent out with the rest of the mutations to attack a major city, in his case Tokyo, Japan. At the end of the "Monster Wars" when all other mutation broke free from the Tachyons control he remained loyal(it is unknown if he was still under their mind control) and returned to Site Omega were he defeated the Giant Vampire Bat and then fought his son Zilla Jr. who chose Nick over him. In the fight he was savagely killed by his son.
Cyber-zilla is a clear homage to all of the Mechagodzillas, especially Kiryu since both of which are cyborgs. He even attacked Tokyo, Japan like them.