Gamera's origin is a bit mysterious. It was said that Gamera was a prehistoric giant turtle whom kind's existence yet to be known by mankind. Some believed that he was the product of nuclear testing, but this statement was false: Gamera was shown capable to absorb nuclear radiation without ill-effects, which means nuclear energy is not his source of powers. In fact, nuclear testing that done near his icy prison was simply energized his body enough to awakened him.
While it appeared that Gamera is a destructive and aggressive monster that deliberately lays waste to Japan after being awakened, Gamera is not truly malevolent due to having soft spot with children and cannot bring himself to harm them in his rampage. This later bring him to the path of heroism since defeating Barugon and seen as hero.
During a dogfight between American and Soviet planes in the arctic, a nuclear bomb was dropped near an iceberg, the explosion causing the ice to split open. Gamera emerged from the iceberg and began approaching Japan. The J.S.D.F. developed a plan to sedate Gamera and destroy him with dynamite. The plan was set into action, but the explosion did not kill Gamera, only knock him onto his back. Just when Gamera appeared stuck, he tucked his head and limbs into his shell, while fire began to spew from the holes. Gamera began to spin like a disc and took flight, flying deeper into the country. As Gamera laid waste to Tokyo, the J.S.D.F. developed a new plan to stop him, codenamed "Plan Z." Gamera is baited into a large rocket, which closes and traps him inside. The rocket then takes off and carries Gamera off into space, saving Japan from the monster's wrath.
Gamera vs. Barugon
Less than a year after being launched into space, the rocket carrying Gamera was struck by a meteorite, freeing the monster. Gamera flew back to Earth and landed in Japan, where he destroyed Kurobe Dam before taking off and flying away again. Meanwhile, an opal brought back to Japan by a thief was revealed to be the egg of a giant lizard called Barugon, which grew even larger from exposure to an infrared lamp. Barugon hatched and rampaged through the Japanese countryside, eventually attacking Osaka. Gamera was attracted by the creature's presence, and confronted Barugon near Osaka Castle. After a brief battle, Barugon froze Gamera solid with his ice breath, then left him for dead in the castle's moat. While Barugon engaged in several confrontations with the J.S.D.F., Gamera thawed and pursued his enemy. Gamera reengaged Barugon near the ocean, overpowering him and dragging him into deep water, where Barugon finally drowned. His enemy vanquished, Gamera flew away without casing any further destruction.
Gamera vs. Gyaos
Gamera appeared during a volcanic eruption to feed on the flames. He then hid in a mountainside until the monster Gyaos appeared from a cave. Gamera fought Gyaos and drove him back into his cave, although his arm was almost cut off. He then saved the child Gyaos was trying to eat and flew him back home. He then returned to the sea to heal his wound. Gamera later returned to attack Gyaos as the creature was attacking a city. He fought Gyaos in the air before he was thrown into the water. He managed to bite off Gyaos' foot before the creature escaped. Gyaos was lured to a container of artificial blood by the J.S.D.F., where the hoped to trap the creature until sunrise, hoping the light would kill the creature. The plan failed, and Gyaos destroyed the trap, producing a fire that attracted Gamera again. This time, Gamera overpowered Gyaos and dragged the creature into the crater of a volcano, killing it. Gamera then flew away, leaving Japan safe.
Gamera vs. Viras
A group of aliens known as Virasians approached Earth, intending to conquer it, but their ship was intercepted and destroyed by Gamera. A group of reinforcements arrived and attached a mind control device to Gamera, forcing him to attack Japan. Two children sabotaged the mind-control, and Gamera turned on the Virasians. The Virasians then combined into their collective form, the giant squid-like monster Viras. Gamera and Viras battled on land and underwater, with Viras eventually impaling Gamera's stomach with its pointed head. Gamera took flight and flew into the atmosphere with Viras stuck to his chest, where Viras began to freeze. Gamera then spun until Viras was detached and plummeted into the ocean below, where it exploded. Victorious, Gamera bid farewell to the children that helped him and flew away.
Gamera vs. Guiron
Gamera came to an alien planet called Terra after a pair of brain-eating aliens captured two boys in their spaceship. Shortly after the Terrans' guardian monster Guiron fought and killed a Space Gyaos, Gamera fought Guiron, and was considered dead after Guiron lacerated his temples with his shurikens. Ultimately, Gamera was revived and confronted Guiron once again. This time, Gamera flipped Guiron upsidedown, sticking his blade-tipped head in the ground, and grabbed a rocket and lodged it into a hole in the side of Guiron's head, then ignited it with his fire breath. The rocket exploded, blowing off Guiron's head. Gamera helped repair the spaceship that brought the boys to Terra, then helped them get back to Earth.
Gamera vs. Jiger
Gamera appeared after a large statue called the Devil's Whistle was removed from an island. Later, the monster Jiger, awakened by the statue's removal, appeared from a volcano, and Gamera arrived to fight her. Jiger fired quills at Gamera, stopping him and allowing her to continue her rampage. Gamera removed the quills and pursued Jiger, confronting her again in Osaka. Gamera held the upper hand in the fight until Jiger extended a stinger from her tail and stabbed Gamera in the chest. Gamera staggered away & fell headfirst into Osaka Bay, where his body slowly began to turn a deathly white. Jiger took the opportunity to toss the Devil's Whistle into the water and resumed her rampage across Japan. A group of children used a mini sub to go into Gamera's body and find the cause of his discoloration. Inside, they discovered that Jiger had infected Gamera with her parasitic offspring. The children fought and killed the baby Jiger and escaped Gamera's body. They then convinced the J.S.D.F. to revive Gamera using electricity. After being revived, Gamera flew to the World's Fair and battled Jiger once again. Jiger used all of her attacks to try and fight off Gamera, but Gamera body-slammed Jiger and stunned her. Gamera then recovered the Devil's Whistle from the ocean and shoved the statue through Jiger's skull, killing her. Gamera then flew back to the island with Jiger's corpse.
Gamera vs. Zigra
Gamera came to the rescue to save a pair of children from the alien invader known as Zigra and his brainwashed human slave Lora Lee. After Gamera saved the children, Zigra took matters into his own hands and revealed himself as a kaiju-sized fish creature. Zigra engaged Gamera in battle underwater, overpowering him with his superiority in underwater combat. Gamera was revived by a bolt of lightning and attacked Zigra again, throwing him onto land, where he was rendered helpless. Gamera used a rock to play his theme song on Zigra's back like a xylophone, then killed Zigra by burning him alive with his fire breath.
Gamera: Super Monster
As the intergalactic criminal Zanon approached Earth with his powerful spaceship, a young boy on Earth purchased a pet turtle from a local pet store. Believing the turtle would be happier in the wild, the boy let his turtle go into the ocean. Miraculously, the turtle transformed into Gamera and prepared to stop Zanon's plan. Zanon sent his agent Giruge to sabotage the Spacewomen's attempts to stop him, while deploying an army of mind-controlled monsters to kill Gamera. Gamera takes on and defeats Zanon's monsters: Gyaos, Zigra, Viras, Jiger, Guiron and Barugon, while Giruge betrays Zanon and sacrifices herself to stop him. Gamera then flies into space and collides with Zanon's ship, sacrificing himself to destroy it.