The Behemoth is one of the three powerful Heartless that were released by the Final Keyhole. The other two leave to attack Neverland and Agrabah, while Behemoth remains and guards the Keyhole. Other Behemoths are also found in the Hades Cup and the End of the World. Sora managed to find all three and defeat all of them.
Kingdom Hearts Re:coded
The Behemoth appears as one of the bosses in Re:coded. It appears in Olympus Coliseum's Layer 25. It is one of four sources of the Bug Blox corruption in the Olympus Coliseum.