The original Godzilla in Godzilla or Godzilla, King of the Monsters! was a prehistoric monster 50 meters tall and weighing 20,000 metric tons that was disturbed by American atom bomb testing in the Pacific Ocean.

After attacking Tokyo, destroying much of the city and killing tens of thousands, Godzilla was defeated when the scientist Dr. Daisuke Serizawa (Akihiko Hirata) commited suicide out of shame and guilt after activating an experimental weapon, the Oxygen Destroyer, which completely dissolved Godzilla. It was stated at the end of the film that it was doubtful that there was only one creature, alluding not only to the many incarnations of Godzilla that would later appear but also to all the other kaiju monsters that would be featured in movies produced by Toho. 

The following series would use the events of the first movie as part of their narrative but would occur in their own continuity separate from each other.