Cyber-Zilla (also known as Cyber-Godzilla) was a cyborg monster, created around the corpse of the first creature that attacked New York in 1998.
After the death of the monster Zilla (called 'Godzilla' by the American media) on the Brooklyn bridge, the creature's body was moved to a secure hangar so the army's scientists could study its remains.
However, when the Tachyon aliens took over the bodies of Dr. Hoffman and Dr. Soppler to begin their invasion of Earth, they took over the minds of all at the base as well as bringing their downed ship up to the surface and rounding up the monsters that Zilla Junior had defeated - including Crustaceous Rex, El Gusano, the Huge Rat, the Queen Bee, King Cobra, Cryptocleidus and later took control of a Giant Bat that Zilla Junior was fighting. Setting up their base on an uninhabited island in the Pacific Ocean - which they referred to as 'Site Omega' - they planned their invasion.
At the base where the first Zilla's corpse was, the aliens resurrected the monster as a cyborg using human and alien technology. Sending the monster after Nick and Craven (who had discovered what was going on), Cyber Zilla was briefly engaged by Zilla Junior. However, Junior's confusion over who is his real father allows the aliens to take control of him - forcing Nick and Craven to once again flee.
After returning to Site Omega, the monsters are soon sent out to begin their attacks on humanity - with the alien's plan being to force humanity to deplete their weapons fighting the monsters before the Tachyon invasion force arrives to take over. Cyber-Zilla is sent to attack Tokyo and is the only monster that remains under the alien's control when H.E.A.T breaks the alien's control over the monsters. Returning to Monster Island, Cyber-Zilla is engaged by the Giant Bat but easily defeats it by using a dish in its chest to reflect the bat's sonic screams back at it.
Zilla Junior soon arrives, and choosing Nick over Cyber-Zilla, attacks the aliens. Although briefly brought down, Zilla Junior revives and battles Cyber-Zilla. In the heat of the battle, Tachyon fighters accidentally blast off the cyborg's mechanical arm. Zilla Junior then blasts Cyber Zilla down before jumping on top of it, ripping out the dish and tearing the wires - killing Cyber-Zilla.
Cyber-Zilla appears in the Godzilla: The Animated Series cartoon in parts 2 and 3 of the 'Monster Wars' trilogy. He is a homage to both MechaGodzilla and Mecha-King Ghidorah, while some say he even inspired the design of Kiryu (MechaGodzilla 3) as both are made around deceased kaiju.
Cyber-Zilla has a variety of abilities. In his cyborg form, he has a mechanical arm, has eight 'energy missile launchers' on his shoulder spines and a disc hidden in his chest that can reflect an enemy's beam attack back at them. In this version, Cyber-Zilla is much tougher than his previous form (been able to withstand Zilla Junior's atomic breath attacks) and also has blue atomic breath, which he didn't have in the 1998 film - presumably due to the Tachyon aliens genetically modifing his D.N.A for this purpose). However, he still retains his running and jumping abilities, his amphibiousness and some amount of 'parental control' over Zilla Junior - enough to cause his 'son' confusion as to who was its real parent.
Due to decay, Cyber-Zilla's skin was a different color while its roar was more metallic. He also had the most violent death in the series, with his arm blown off and body ripped open. When Zilla Junior tore out the wires and caused the cyborg to short circuit, Cyber-Godzilla even gave a final 'death rattle' before dying.