Gigan's first appearance was in the 1972 film Godzilla vs. Gigan. In the film, Gigan is summoned to Earth by the antagonist Nebula M Space Hunter aliens where he was paired with the three-headed space dragon King Ghidorah to destroy Tokyo. They were challenged by Godzilla and Anguirus, and after a long fight the two space monsters were driven away.
In the 1973 film, Godzilla vs. Megalon, Gigan was sent by the antagonist Nebulans to assist the people of Seatopia in their assault on humanity by aiding their god, Megalon, in a battle against Godzilla and the robot Jet Jaguar. After receiving a broken arm at the hands of Jet Jaguar, Gigan fled to space, leaving his erstwhile ally Megalon to face Godzilla and Jet Jaguar alone. This is the second time Gigan has abandoned an ally. This seems to indicate that Gigan has a traitorous personality.
Also in 1973, Gigan made an appearance on Toho's television series Zone Fighter. Gigan was defeated by Godzilla once again. Left for dead by Godzilla, Gigan was revived later to battle Zone Fighter. In the final battle, Gigan is killed by Zone Fighter, making him the only Godzilla monster to have been introduced in the main movie series but whose death is only shown in another media.
Gigan's latest appearance was in the 2004 Millennium film, Godzilla: Final Wars, where he is one of the main antagonists for Godzilla to fight. After Gigan is beheaded and seemingly killed by Godzilla, his alien masters recover and rebuild his body, upgrading him with claws designed like double pronged chainsaws. This time, Gigan is killed by Mothra, who sacrifices her life to kill the ancient cyborg.
 Powers and abilities Hooked arms Gigan's forelimbs sport a pair of large metal hooks in place of hands which the monster uses to both batter and stab his opponents. In his appearance on the television series Zone Fighter, the tips of the hooks can release an explosive charge on contact with an enemy. In Godzilla: Final Wars, Gigan's arms were replaced with chainsaws after being defeated by Godzilla.
Antigravity flight Gigan has a trio of retractable wings which is capable of allowing Gigan to fly at speeds of up to Mach 3. This normally assists in interstellar travel and is utilized very little, if at all, during battle situations. When it is used in battle, however, Gigan will often use it to engage in aerial slams to continuously topple his opponents without giving them a chance to counter, or even get up. In Godzilla: Final Wars, the antigravity flight was replaced by jetpacks, presumably to give Gigan more of a robotic feel.
Teleportation In Godzilla: Destroy All Monsters Melee, Godzilla: Save the Earth, and Godzilla: Unleashed, Gigan has the ability to teleport in a green flash.
Buzzsaw Gigan has a buzzsaw built into his abdominal area. It is of considerable durability and effectiveness as it was sharp enough to cause severe epidermal damage to Godzilla and Anguirus (being the first weapon shown to breach Godzilla's skin and actually draw blood) and brought down a weakened Gotengo.
Grappling cables In Godzilla: Final Wars, Gigan was able to fire two hooked grappling cables from beneath both of his hand blades which he used to snag onto his opponents and reel them into range of his deadly buzzsaw.
Razor discs In Godzilla: Final Wars, the upgraded Gigan was able to fire two razor sharp disks from just above his buzzsaw. Mothra however dodged them and simultaneously released her reflective powder, which caused them to malfunction and boomerang back towards Gigan who was promptly decapitated the second time in that movie.
Eye beam In Godzilla: Final Wars, Gigan could fire a red beam from his eye that scattered into a shot-gun like blast of energy. It should be noted that Gigan can be seen firing his eye beam in poster artwork for Godzilla vs. Gigan and Godzilla vs. Megalon, yet he never uses this ability in those films.