The Behemoth is mentioned in Job 40:15-24 as described by God:
Behold now behemoth, which I made with thee; he eateth grass as an ox. Lo now, his strength is in his loins, and his force is in the navel of his belly. He moveth his tail like a cedar: the sinews of his stones are wrapped together. His bones are as strong pieces of brass; his bones are like bars of iron. He is the chief of the ways of God: he that made him can make his sword to approach unto him. Surely the mountains bring him forth food, where all the beasts of the field play. He lieth under the shady trees, in the covert of the reed, and fens. The shady trees cover him with their shadow; the willows of the brook compass him about. Behold, he drinketh up a river, and hasteth not: he trusteth that he can draw up Jordan into his mouth. He taketh it with his eyes: his nose pierceth through snares.
The depictions of Behemoth range anywhere from a mythical creature to an elephant, hippopotamus, rhinoceros, or crocodile - or even a combination of them. Some creationists even believe that the description refers to a sauropod, an enormous dinosaur, due to its tail being described like a cedar tree.