Otherwise known as the great whale of the Disney Seas, Monstro is a large whale that has since been corrupted by the heartless, and is under their influence, although he was still infamous even before he became under the control of the heartless. He is known for taking down and destroying entire fleets, even before the Heartless took him. After ingesting ship wreckage, cages containing heartless were broken, releasing the Heartless into Monstros body. This was one of the first recorded incidents of heartless showing signs of intelligence, as, instead of taking Monstros heart, they manipulate his body, using him as a vehicle for the heartless within.
Although the heartless have left Monstros heart relatively intact, his internal organs and body have been warped and disfigured because of the nature of the dark corruption. Fungus and parasites grow almost everywhere, due to the moist and decaying nature of his body.
Use by the Heartless
The heartless inside use Monstro to attack ships and marine wildlife, and then, once damaged enough, Monstro swallows the surviving crew members and wildlife. Apon being swallowed, the heartless will attack the survivors, then consuming their hearts.