In the
Kingdom Hearts series, he was the first apprentice of
Ansem the Wise, having been discovered "on death's door" and afflicted with amnesia when he was young. He was
Ansem's first test subject, and carried
Ansem's experiments further than advised, even though he and the others were forbidden from any more experimentation and ordered to destroy the results of their past research. He eventually stole
Ansem's identity and became a
Heartless and a
Nobody along with the others. His
Nobody is
Xemnas, the leader of Organization XIII. His
Heartless was known as
Ansem, but is simply
Xehanort's Heartless.
Sora wasn't very happy to find out that the man he thought was Ansem was really the Heartless of his apprentice, Xehanort.