Gyaos

Gyaos is considered to be Gamera's archenemy, and has made more film appearances than any of his other enemies. In the Showa series, Gyaos was Gamera's second foe, and emerged from an underground cave to feed on humanity. Gamera battled the creature in several encounters, finally destroying it by pulling it into the crater of an active volcano. However, Gyaos was not the only creature of its kind, as multiple silver Space Gyaos were a frequent nuisance on the alien planet Terra in the film Gamera vs. Guiron. The Terrans' guardian monster Guiron fought and brutally killed one Space Gyaos by chopping it apart with its head blade. In Gamera: Super Monster, Gyaos was one of the monsters controlled by the sinister crew of the pirate spaceship Zanon, which it used to menace humanity and try to defeat Gamera.

In the Heisei trilogy of films, Gyaos was reinvented as a perfect organism genetically engineered by the ancient Atlanteans. Gyaos began reproducing out of control and turned on their creators, who created Gamera as a last-ditch effort to stop them. Gamera succeeded in killing most of the Gyaos, but clutches of their eggs survived into the modern day, where changing environmental conditions brought on by human activity caused them to hatch. Gamera reemerged as well to battle his ancient foe, and successfully killed three Gyaos that appeared in Japan in 1995. However, countless more Gyaos would appear in 1999 as a result of Gamera depleting Earth's mana in order to destroy Legion. These evolved Hyper Gyaos began overrunning the world, with Gamera desperately trying to defeat them. After Gamera defeated the creature known as Iris, an ancient demonic beast genetically related to Gyaos, a swarm of thousands of Gyaos descended on Japan to attempt to destroy Gamera once and for all.

In the most recent Gamera film, Gamera the Brave, a flock of four Gyaos attacked a Japanese village in 1973, but were attacked by Gamera, who was forced to self-destruct and sacrifice himself in order to kill them. A new monster called Zedus was eventually spawned by feeding on the corpses of the flock of Gyaos, and did battle with the reincarnation of Gamera three decades later.