1350–1400; < Hebrew bəhēmōth, an augmentative plural of bəhēmāh beast; replacing Middle English bemoth

The original behemoth is found in the Bible. Job 40:15-24 describes a land-dwelling beast having mythic proportions (a tail like a cedar tree) and supernatural characteristics (bones like bars of brass and iron). The Hebrew word that is used ( bəhēmōth ) is the augmentative plural form of the word for “beast” or “animal.” Normally, bəhēmōth would translate as the plural noun “beasts,” but as it is used to describe a singular being, the interpretation is that of a mighty or monstrous animal.
Much folklore has arisen around behemoth. One story has it that behemoth, separated from its aquatic counterpart leviathan at the dawn of creation, will be reunited with it in an epic battle on Judgment Day in which each will slay the other. Following this biblical King Kong vs. Godzilla match, both animals will be served up as a feast for the remaining faithful.
Behemoth makes an appearance in such classics of literature as John Milton's Paradise Lost, Shelley's Prometheus Unbound, and James Joyce's Finnegans Wake. Today we use it to apply to anything large, powerful, and often unwieldy.

— Behemoth: Thomas Hobbes's 1681 book on the English Civil Wars, from the Scottish revolution in 1637 to the Restoration of the Monarchy in 1660.
—Behemoth: A character in The Master and Margarita by Mikhail Bulgakov. Behemoth is a walking, talking, gun-toting black cat, and a demon in disguise.
—Behemoth: A Polish rock band, playing what's known as blackened death metal, a mix of black metal and thrash metal music.
—The Behemoth: A video game development company, creators of the popular video games Alien Hominid (2004) and Castle Crashers (2008).
— Behemoth: The second book in Scott Westerfield’s steampunk young adult series, published in 2010.