Godzilla

It is speculated that Godzilla may have been the "big green, fire-snortin' lizard" mentioned in passing by S.H.I.E.L.D. employee Nicholas in issue #3 of the Marvel comic.

Unrelated to the above, Godzilla is responsible for taking a bite out of Optimus Prime, like Scruff McGruff took a bite out of crime, of in the non-canonical flash animation "Ultimate Battle of Ultimate Destiny".

From Teletraan I: The Transformers Wiki, a Wikia wiki.