Leviathan (Hebrew לִוְיָתָן, Livyatan) is the sea-serpent of the Hebrew Bible — a chaos-monster of the deep that God subdues. In Psalm 74:14, God smashes Leviathan's heads in the waters. Isaiah 27:1 announces that the Lord will slay "Leviathan the fleeing serpent, Leviathan the twisting serpent." Job 41 describes the creature at length and in awe. Etymologically Leviathan is connected to the Ugaritic Lotan, the seven-headed sea-monster Baal defeats in the Baal Cycle — making him one of the clearest surviving traces of Chaoskampf in the Hebrew Bible, the older combat motif preserved in poetry and prophecy even after Genesis 1 demythologized it. Later Jewish and Christian apocalyptic literature took Leviathan up as an eschatological figure.
The ancient Near Eastern combat motif Leviathan is one of the clearest Hebrew traces of.
The other Hebrew chaos-monster — named alongside Leviathan in Psalm 89 and Isaiah 51.
The Babylonian saltwater goddess slain by Marduk — the eastern cousin of the same sea-monster pattern.
Reading Genesis 1 slowly, with the surviving chaos-monster traces in the rest of the Hebrew Bible in view.