Behemoth is a beast from the biblical Book of Job, and is a form of the primeval chaos-monster created by God at the beginning of creation. Metaphorically, the name has come to be used for any extreme
Behemoth as depicted in the Dictionnaire Infernal by Collin de Plancy
Leviathan the sea-monster, with Behemoth the land-monster and Ziz the air-monster. "And on that day were two monsters parted, a female monster named Leviathan, to dwell in the abysses of the ocean over the fountains of the waters. But the male is named Behemoth, who occupied with his breast a waste wilderness named Duidain." (1 Enoch 60:7–8)