The Heartless are hearts corrupted by darkness. When a Heartless takes the heart of a human, the darkness in that heart is reborn as a Heartless. Ansem Report 7 from KH2 gives a lot of information on the Heartless, and here is a portion of it: "They simply seek out hearts and gather. For a human's heart, all they do is they easily remove the heart and take it into themselves, creating more companions. They do not listen to the orders of humans. But, what about the orders of stronger Heartless? If, for example, that man discarded his soul and body to become a Heartless, could he not lead the naturally unleaderlike Heartless? Furthermore, does he intend to take advantage of the Heartless' instinct? If the Heartless, who seek out hearts, are aiming for a bigger, stronger heart, the final objective is clear. In this world, the greatest heart is...'the heart of the world'"
 The Heartless
 Air Pirate
Winged Heartless that mostly appear in Neverland. They are extremely combative and are hardly ever caught off guard. They attack with martial-arts-like techniques.
 Air Soldier
Winged Heartless. They fly over their enemies and dive to strike them. Their high endurance and quickness make them tough to beat.
 Angel Star
Flying Heartless that cast potent spells. They are born of holy spells. They attack from long range with magic. They block physical attacks with their wings, making them difficult to defeat.
Heartless that mostly appear in Agrabah. They can travel under the sand. They attack deftly with a long sword. Attack them with caution.
Heartless resembling a fish that calmly swim the seas. They are often carry Screwdivers. Leisurely large creatures that do not attack unless provoked.
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