Guiron is a genetically-engineered alien monster that serves as the Guardian of the planet Terra - a planet in our solar system which humanity had not yet discovered as it orbits the sun directly opposite the Earth. He appears as the main antagonist of the Showa era Gamera movie, Gamera vs. Guiron, and as a minor antagonist in the Showa era Gamera movie, Gamera: Super Monster.
Guiron was a frog-like monster with a huge knife on his head. - stated to be 100 times harder then diamond. Guiron is also capable of a ranged attack, as it can fire a total of four shruikens out of a pair of circular indents on his blade.
Guiron himself is controlled by a mind control device - his 'masters' being a pair of Terran women called Barbella and Florbella who are the last of a dead civilization. When two boys from Earth unintentionally end up on Terra, they watch as Guiron battles Space Gyaos - easily and brutally killing the creature - before retreating. The boys are soon captured by the two Terran women - revealed to be the last members of their race - who are actually cannibals and plan to eat the boy's brains. However, they are forced to deploy Guiron as Gamera arrives on the planet, looking for the two boys. The first battle between the monsters ends in a draw, with both wounded.
As the boys try to escape, they unintentionally release Guiron again - this time not under mind control. Unrestrained, Guiron attacks everything in sight and even attacking a spacecraft with the two Terran women on board as they attempt to flee to Earth. Only Barbellla emerges - having killed Florbella when she was injured as in Terran society, "useless members" of their people are euthanized. Gamera soon returns and saves the boys from an attack by Guiron, managing to pin him in the ground upside down, while the other Terran woman is killed as half of a missile strikes the station she is in - blasting it apart.
Taking one half of the still functioning missile, Gamera throws it into Guiron's open shruiken base before using his fire breath on the missile. The missile explodes - blasting Guiron in half and finally killing the monster. Gamera then takes the boys back home to Earth - with Terra seemingly abandoned to the Space Gyaos.
Guiron would later be revived by the evil aliens known as the Zanon - as part of their plan to conquer Earth. This would lead to another battle with Gamera on Terra. However, Guiron would once again lose - this time dying for good.
Gamera vs. Guiron - Movie
Gamera: Super Monster - Movie