The Behemoth is a mythical beast that is mentioned in Job 40:15-24. It is said to be a gigantic ox-like beast with bones as hard as bronze and limbs as firm as rods of iron.
Behemoth in the Bible
Job 40:15-24 describes the Behemoth as God is speaking to Job. According to the passage, the Behemoth is an ox-like creature that feeds on grass, yet is so large that his tail is the size of a ceder tree. Some argue that the Behemoth was the first of God's creations because Job 40:19 calls it "first among the works of God."
15 Look at the behemoth, which I made along with you and which feeds on grass like an ox.
16 What strength he has in his loins, what power in the muscles of his belly!
17 His tail sways like a cedar; the sinews of his thighs are close-knit.
18 His bones are tubes of bronze, his limbs like rods of iron.
19 He ranks first among the works of God, yet his Maker can approach him with his sword.
20 The hills bring him their produce, and all the wild animals play nearby.
21 Under the lotus plants he lies, hidden among the reeds in the marsh.
22 The lotuses conceal him in their shadow; the poplars by the stream surround him.
23 When the river rages, he is not alarmed; he is secure, though the Jordan should surge against his mouth.
24 Can anyone capture him by the eyes, or trap him and pierce his nose?
The Behemoth in Jewish Legend
Just as the Leviathan is an unconquerable monster of the sea and the Ziz a monster of the air, the Behemoth is said to be a primordial land monster that can't be defeated. According to the 2nd century B.C.E. Book of Enoch, he lives in an desert "east of the garden where the elect and righteous dwell" (1 Enoch 60:7-8). At the end of time the Behemoth will do battle with the Leviathan and both will be killed. According to some legends, the Behemoth will be an entree served at the messianic banquet in Olam Ha Ba (the World to Come). In this instance, Olam Ha-Ba is conceived of as a Kingdom of God that will exist after the Messiah comes.
Sources: I Enoch, Book of Job and "The Encyclopedia of Jewish Myth, Magic and Mysticism" by Rabbi Geoffrey W. Dennis.