Godzilla is...

All of the Above

Selfin Dragon

1. A giant radioactive iguana.
A member of the Iguanidae family (Tatopoulos said the design is based off of his pet Selfin Dragon), Godzilla of 1998 (hereby referred to as Zilla) would be born from the blast of radiation from nuclear testing. This would be the only similarity Zilla would share with the origins of Classic Godzilla.

Nuclear blast from Hiroshima

2. An allegory for the bomb.
The original Godzilla emerged as a representation of the horrors that the Japanese people experienced at the bombing of Hiroshima and Nagasaki in 1945. Godzilla would become a symbol of the bomb, seeing as how the Japanese never tested nuclear weapons, but were only the victims of an unstoppable force. Godzilla became that unstoppable force, destroying Tokyo overnight, and leveling the city like the bomb had done to Hiroshima and Nagasaki. The fear of the invisible killer, radiation, was real to the Japanese audience and Godzilla presented the opportunity to make that fear visible. He was given a radioactive beam, a character trait that would become iconic with Godzilla.

Godzillasaurus

3. A Godzillasaurus
In order to revive the series and give Godzilla a new look, the writers would go back and change Godzilla's origin. Godzilla vs. King Ghidorah (1991) would have Time-travelers from the future come back and move the 1944 Godzillasaurus on Lagos Island to the Bearing Sea, therefore avoiding creating the original Godzilla at all. However, the Godzillasaurus was exposed to radiation from a nuclear submarine and is reborn bigger, stronger, and meaner than ever. Godzillasaurus resembles a typical theropod but with a double set of teeth, which is later reflected in Godzilla from the Heisei series.

4. A Force of Nature.
Godzilla has been and always will be a force of nature. Looking at any of Godzilla's origin stories, he is still an animal. Transformed into a towering force, imbued with radioactive properties, and being the last of his kind, Godzilla faces a world that he can never be a part of. Acting like any animal would, Godzilla is merely defending his territory. He is neither good, nor bad, but a neutral force (this topic will be discussed in later days).