Swampy

Swampy the Crocodile, often referred to simply as Swampy, is the main antagonist of Frogger 2: Swampy's Revenge. He is apparently one of the crocodiles that is repeatedly stepped on in the original arcade game. This is further supported as his official bios states that he's "our for revenge", referring to Frogger.

Frogger 2: Swampy's Revenge
"Swampy the Crocodile is sneaky, brutish, sly, greedy and above all dastardly! Swampy doesn't like frogs. In fact, Swampy doesn't like anything much, least of all Frogger. He's out for revenge and his plans involve the frog babies. But just what is he up to?"

Trivia

 * Since Swampy is playable in Frogger 2, you can have two Swampys on the screen at the same time in Space Chase.