Ansem, Seeker of Darkness

Xehanort (ゼアノート, Zeanōto?) is an original character created for the Kingdom Hearts series, serving as the primary antagonist of the Xehanort Saga. Xehanort is a student of Ansem the Wise, who becomes increasingly obsessed with the study of hearts it as he regains some of his lost memories. To that end, he sacrifices his body in the process, creating his Heartless and Nobody.

His Heartless assumes the identity of his teacher, Ansem, while his Nobody takes the name Xemnas. "Ansem" is featured in Kingdom Hearts as the main antagonist. He commandeers the heartless to do his bidding and steals the hearts of many worlds. Late in the video game, he takes Riku's body to regain a physical presence. Although his goal of reaching Kingdom Hearts is realized, the light behind the door to Kingdom Hearts destroys him, causing all of the worlds he destroyed to be restored. However, In Kingdom Hearts: Chain of Memories, "Ansem" is revealed to still exist and attempts to take over Riku's body again. But Riku manages to defeat him, assuming his form later on while able to maintain control.