Godzilla is a kaiju who first appeared in the 1954 film Godzilla.
The original Godzilla is a prehistoric amphibious sea creature that was disturbed and burned when an American hydrogen bomb test conducted in the Pacific Ocean destroyed his habitat and drew him to the surface. Godzilla unleashed his rage upon humanity, destroying any ships in his vicinity and eventually laying waste to Odo Island and the city of Tokyo. Daisuke Serizawa eventually used his invention, the Oxygen Destroyer, to kill Godzilla, while taking his own life to ensure the weapon could never be used again.
In several of the Godzilla films' continuities, a second Godzilla appears sometime after this one's death. The only film connected to the original which does not feature a second Godzilla is Godzilla vs. Megaguirus, which instead takes place in an alternate reality where its version of the first Godzilla never died and continues to menace Japan. The First Generation Godzilla's remains also appear in the film Godzilla Against Mechagodzilla, in which they are salvaged by the Japanese government and converted into a bio-robot dubbed Kiryu in order to battle against a second Godzilla.