The "Fire Demon," or Rodan, was a massive winged Titan that had a thing for molten rock and active volcanoes. Ancient people feared him because he could destroy whole towns by flying above them. Rodan settled inside the magma-filled volcano crater on the island that would become Isla de Mara in Mexico. By 1973, thanks to research into ancient cave drawings showing Rodan and other Titans like Godzilla, Mothra, and King Ghidorah, the scientific organization Monarch — created in the wake of World War II to study and hunt for Titans — had learned of Rodan's existence. In 1991, Monarch discovered Rodan dormant in pyrostasis inside the Isla de Mara volcano and established Outpost 56 to investigate and imprison him.
The Japanese name for Rodan is Radon, short for "Pteranodon." It might have been picked to allude to radioactivity as well. It's possible that the similarity between the katakana forms of Radon and Ladon, a dragon-like creature from Greek mythology, is only a coincidence. In English-speaking regions, the name was changed to "Rodan" to prevent consumer confusion with the element radon. After some time, Toho trademarked the word "Rodan," making it the official English name for the monster. But in the English versions of Terror of Mechagodzilla and Godzilla vs. Mechagodzilla II, the name "Radon" was adopted. This was also the case with Invasion of Astro-Monster.
