The Leviathan is some kind of Shark-whale-eel-lobster monster that is really big. It was created by the Demon Penguins. It enjoys making sand castles and is known to sometimes eat Burger Khan (The Entire building with customers, and employees. And burgers, we can't forget the burgers!). It is one of the Freakishly Big Demonic Monsters of Destruction
The Demon Penguins felt like they needed a giant monster to help with the nave. They decided to combine the DNA of a shark, eel, whale, and lobster to create the ultimate sea monster. However, they were thinking reall big and decided to make the creature thousands of feet long. They did that and the Leviathan was created.