Heartless

The Heartless are a race of cretures from the video game series, Kingdom Hearts.

Origins
The Heartless are born from darkness. When a heart is stolen, the darkness in it consumes the heart, forming a heartless. The body and soul then form what is called a Nobody. Pure heartless are born directly from hearts, but seal heartless are born from a machine that collects darkness.

Ansem's Studies
Ansem the Wise, ruler of Radiant Garden, studied the heartless.

Ansem's Reports
The Ansem Reports can be collected by Sora throughout the games. They were written by Ansem and contain information on the Heartless. In Kingdom Hearts II, they also contain information on Organization XIII.

Xehanort
Ansem's six apprentices aided in the study of the heart. The apprentices became corrupted by the darkness. They're leader was Xehanort. The apprentices all became heartless and their nobodies formed the group, Organization XIII. They also created a machine that created Heartless and branded them with a special seal.