So what’s the deal with this scary sea monster, ‘Leviathan’, that Job and the Psalms talk about?

Well Leviathan is an embodiment of chaos. And it’s an idea the biblical writers absorbed from the culture around them, particularly from Ba’al religion.

Both the name and the mythological figure are a direct continuation of the Ugaritic sea monster Lôtān, one of the servants of the sea god Yammu defeated by Hadad in the Baal Cycle

His role seems to have been prefigured by the earlier serpent Têmtum whose death at the hands of Hadad is depicted in Syrian seals of the 18th–16th century BC.

Sea serpents feature prominently in the mythology of the ancient Near East.[12] They are attested by the 3rd millennium BC in Sumerian iconography depicting the god Ninurta overcoming a seven-headed serpent.

It was common for Near Eastern religions to include a Chaoskampf: a cosmic battle between a sea monster representing the forces of chaos and a creator god or culture hero who imposes order by force.