Godzilla

It is speculated that Godzilla may have been the "big green, fire-snortin' lizard" mentioned in passing by SHIELD director Nicholas Fury in issue #3 of the comic.

In the non-canonical and unfunny flash animation "Ultimate Battle of Ultimate Destiny", Godzilla is responsible for deactivating Optimus Prime by biting his head off.

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