I don’t know how you would describe Godzilla, or to whom, but I might describe Godzilla to someone who had never heard of him (if I were ever to meet such a person) as:
Imagine someone is a rubber dinosaur suit that is like an upright Stegosaurus with a head a bit more like that of a Tyrannosaurus Rex, who’s supposed to be taller than tall buildings and amphibious and had radioactive jet breath. He’s nearly invulnerable and sometimes goes on a rampage and does lots of damage to cities, but is really also a beloved hero who saves more people by fighting other giant monsters. Many films have been made about him, mostly in Japan, which tell different versions of his story and what he is like.