Ansem

Ansem the Wise was a famous scientist and sage-king of Radiant Garden. To protect his people from the darkness, he and his apprentices performed research and experiments to study the heart, which resulted in the creation of the Heartless. Eventually, Ansem's apprentices were taken over by the darkness, and, when he decided to end the research, they banished him to the Realm of Darkness and Xehanort continued the research in his name.