Showa
In Godzilla vs. Mechagodzilla, King Caesar was the guardian of the Azumi family. He could be awakened by fulfilling a prophecy and an ancient song.
The Simians knew about Caesar and that it would awaken to prevent them from attempting world domination. When their Mechagodzilla was repaired after being damaged, the aliens sent the cyborg to conquer the Earth once more.
King Caesar was awakened and he confronted the robot. At the beginning, Caesar was able to successfully fight back by reflecting the cyborg's laser beams through his own eyes and then reflecting the projectiles back at his adversary. However, Mechagodzilla was too strong even for the guardian and almost defeated Caesar.
However, Godzilla arrived to aid King Caesar. Still, Mechagodzilla was more powerful than both of them and horribly outmatched the duo. Godzilla, who had been struck by lightning repeatedly prior to this battle, converted that electrical power into an electro-magnetic attraction ability, essentially becoming a living super electro-magnet during the fight and used it to pull Mechagodzilla towards him when the latter attempted to flee when it began to run low on power and ammunition. Godzilla held his robotic clone in place, allowing Caesar to ram the giant robot repeatedly. Godzilla finished off the machine by ripping off its head, and fell into the sea when Mechagodzilla's body exploded. King Caesar then returned to the rock formation from where he emerged. The alien base built into the mountain then self-destructed, sealing the entry and allowing King Caesar to rest peacefully until he would be needed again.
Read more about this topic: King Caesar, Origins