Behemoth is a powerful Heartless from Kingdom Hearts. It was one of three powerful Heartless released by the Final Keyhole, which is also the Keyhole to Hollow Bastion. The other two were Phantom and Kurt Zisa. While the other two left to destroy Neverland and Agrabah, the Behemoth remained and guarded the keyhole. Donald witnessed the two other heartless leaving the keyhole, but said nothing.
There were multiple Behemoths; although the first Behemoth was found in Hollow Bastion, other Behemoths were found in the Olympus Coliseum and End of the World. They were all battled the same, though. Sora sometimes battled Destroyed and Arch variants.
"Bull-like heartless appear into that world of darkness. Apprentice of worlds mayhem of burning Darkballs."
Despite its "storyline" strength, the Behemoth can be defeated relatively easy, compared to many other bosses. Its only weakness is its horn, growing from its head, which is more often than not out of the player's reach while standing on the ground. The "trick" is to jump on to the thigh of one of its hind legs and then further on to its back (or just directly onto its back, if possible), and then simply run up to the back of the horn to avoid falling of due to the Behemoth's head movements. From this position, one can attack freely, and without the possibility of being attacked by the Behemoth. Also, ice, thunder, and fire magic does not effect it.
- Two Behemoths were seen during the War of 1000 Heartless. However they were not part of the battle, because they were considerd too hard.
- The Behemoth fought in Hollow bastion is one of three heartless released from the final Keyhole, the others being Kurt Zisa and Phantom