The two creatures are described at length in the speech that closes the book of Job, where God answers a man demanding justice with a tour of the parts of creation he did not make and cannot control. Behemoth comes first: an animal that eats grass like an ox, whose strength is in its loins, whose tail stiffens like a cedar, that lies under the lotus in the reeds and is not disturbed if a river rages. Leviathan follows at greater length, and the description is deliberately overwhelming. No hook will hold him, no harpoon will pierce his hide, his sneezing flashes light and his eyes are like the eyelids of the dawn, smoke comes out of his nostrils, he makes the deep boil like a pot, and on earth there is nothing like him, made without fear.
Elsewhere the imagery is combative rather than descriptive. A psalm speaks of God breaking the heads of the sea monsters in the waters and crushing the heads of Leviathan, giving him as food to the creatures of the wilderness. A passage in Isaiah looks forward instead, promising that on that day God will punish Leviathan the fleeing serpent, Leviathan the twisting serpent, and will kill the dragon that is in the sea. The language of a sea-dragon defeated at the founding of the world is shared with older Canaanite and Mesopotamian material, where the same or a closely related creature appears under names including Lotan, and the comparison is one of the most heavily worked in the study of Israelite religion in its regional setting.