Calvin has appeared as a Godzilla alter ego in a weekday strip and a Sunday strip. Godzilla is the only one of Calvin's alter egos to be a copyrighted character, although his superhero alter egos have borne similar traits to various comic book protagonists.
In the alter ego's first appearance, Calvin smashed an (inaccurate) Tokyo replica in his sandbox while pretending to be a rampaging Godzilla.
In his second appearance, Godzilla appeared when Calvin breached from his bath and went downstairs to attack his mother , whom he perceived as "his arch-rival Megalon". The latter is an actual rival of Godzilla from 1973's Godzilla vs. Megalon.