Mecha-King Ghidorah is a mechanically modified version of King Ghidorah who a mechanical head, torso, wings, and a few other areas. He appears in the 1991 film, Godzilla Vs. King Ghidorah. He serves as the titular main antagonist in his original form and when he becomes Mecha-King Ghidorah, he serves as a protagonist to battle the new titular main antagonist.
Godzilla vs. King Ghidorah
After Ghidorah's death at the hands of Godzilla, the King of the Monsters proceeded to wreak havoc on Japan. Emmy Kano, a Futurian who rebelled against her crew, was asked if she could revive Ghidorah and bring him back to stop Godzilla. Emmy complied and used her time-travel machine, the KIDS, to travel to the future.
As Godzilla rampaged through Japan, he heard a noise. Mecha-King Ghidorah, pilotted by Emmy Kano, appeared in a pulse of energy. The two titans clashed. Ghidorah fired his gravity beams and laser triple beams at Godzilla, who retaliated by firing his thermonuclear ray. Mecha-King Ghidorah then knocked Godzilla into a building. Godzilla countered by damaging Ghidorah's wings. Deciding to finish the battle, Ghidorah released capture cables and grabbed Godzilla before carrying him out to sea. Godzilla hit Ghidorah with a blast from his thermonuclear breath and sent them both crashing into the ocean, where they both remained. Godzilla would escape while Mecha-King Ghidorah's robotic parts would be used to build Mechagodzilla.