Megalon is a large cockroach/beetle based kaiju controlled by the Seatopians and the primary antagonist of the 1973 Godzilla film, Godzilla vs. Megalon.
Megalon was the guardian of Seatopia, an underwater kingdom, that suffered from the nuclear testing and pollution of the people in the surface world. They summoned Megalon to make the people pay by attacking Japan. The monster began wreaking chaos throughout the country but was soon opposed by a robot known as Jet Jaguar. The Seatopians had stolen the robot previously to help Megalon, but its owner had freed it from their control. Jet Jaguar was able to outmatch its foe and the Seatopians asked the Nebulans to send Gigan to help Megalon. The two were able to overpower Jet Jaguar and were close to destroying the robot, but Godzilla arrived and helped the robot drive the two away. Gigan fled back into space and Megalon burrowed back underground, where it has stayed ever since.
- Even though Godzilla vs. Megulon was a critical and financial failure, Megulon remains a popular character in the Godzilla franchise, being a playable character in multiple games, including Godzilla: Destroy All Monsters Melee, Godzilla: Save the Earth, and Godzilla: Unleashed.
- Megalon is one of the three Godzilla kaiju villains from the Showa era to never reappear in a later film, the other two being Gabara and Titanosaurus.
- Originally, Megalon was suppose to make his debut in the unmade film Godzilla vs. the Space Monsters: Earth Defense Directive. In the film, Megalon, along with Gigan and King Ghidorah, would be the pawns of an evil alien brain called Mako in its conquest to rule the universe and fought against Godzilla, Anguirus, and a stone statue kaiju called Majin Tuol to take over the Earth.
- Following the film's cancellation, Megalon was selected to be the villain for the film Jet Jaguar vs. Megalon. However, Toho feared that Jet Jaguar did not have enough value to guarantee the film's success, so Godzilla and Gigan were added into the film in the process.