The demon in the Bible often depicted as a sea serpent and symbol of chaos is Leviathan.
Leviathan appears in the Hebrew Bible, especially Job 41, Psalms, and Isaiah. Job portrays it as an immensely powerful sea creature that humans cannot subdue, while Isaiah calls it a twisting or fleeing serpent destined for destruction. These passages helped establish Leviathan as a symbol of untamable forces and cosmic disorder.
The figure likely reflects older West Asian sea-monster traditions. Leviathan is closely related to the Ugaritic Lotan, a serpent defeated by the storm god Baal, and is often compared with Mesopotamian Tiamat. Those parallels explain why later interpreters connected Leviathan with primordial chaos.
Leviathan is not simply interchangeable with Behemoth: later Jewish tradition generally places Leviathan in the waters and Behemoth on land. Christian demonology eventually associated Leviathan with the deadly sin of envy, giving the biblical monster an additional demonic identity.