The leviathan is a huge and fierce water monster/sea serpent, talked about mostly in the Bible and Old Testament. Many say leviathan simply means "whale", or any huge water creature. It is scaly with fierce fangs. Many compare a leviathan to a crocodile, and some say that leviathans are described as breathing fire, such as dragons. People believe that a leviathan is merely a Plesiosaurus, a large reptile that lived during the Jurassic period, and could also be called the Loch Ness monster. A leviathan is known to control the water and all who dwell in it.

"Who dares open the doors of his mouth, ringed about with his fearsome teeth? His back has rows of shields tightly sealed together; each is so close to the next that no air can pass between. They are joined fast to one another; they cling together and cannot be parted. His snorting throws out flashes of light; his eyes are like the rays of dawn. Firebrands stream from his mouth; sparks of fire shoot out. Smoke pours from his nostrils as from a boiling pot over a fire of reeds. His breath sets coals ablaze, and flames dart from his mouth. Strength resides in his neck; dismay goes before him. The folds of his flesh are tightly joined; they are firm and immovable. His chest is hard as rock, hard as a lower millstone. When he rises up, the mighty are terrified; they retreat before his thrashing. The sword that reaches him has no effect, nor does the spear or the dart or the javelin." - Job 41:1-34 (This is Wikipedia's revision of this statement from the Bible.)