Well i think it was first said by Ben Franklin (not 100% though) he was the first person to use it. he recored it because he thought it sounded clear.
a bit more trivia now 😛
before that no one used it. The closest word to it was 'Hullo' with a 'U' instead of the 'E' and this was not used as a greeting but a word used to show shock. (for example hullo the dog has eat my food).
If i am reading this question right then i think the answer is he was the consequence of a hydrogen bomb test to see what the affect would be on earth. But i don't know if you were asking that or where the idea of Godzilla originated 😖
If that is what you meant then the next question sticking with movies is what was the name of the 1st dinosaur ever in a movie ?
If it iss not right though then i have no idea 😖