Xehanort is a major antagonist of the Kingdom Hearts series, a former apprentice of Ansem the Wise, and the original persona of Ansem Seeker of Darkness, and Xemnas. Xehanort was originally "born" as Terra-Xehanort, when his original incarnation, Master Xehanort, transferred his heart into the body of Terra, but became simply "Xehanort" when his personalities and memories were sealed within his heart. He is the main antagonist of the Xehanort Saga, and has made an appearance in every game in said saga so far, in some shape or form. Similar to the Organization XIII members, Xehanort's name contains the letter "X", along with anagrams for "No Heart" and "Another".
~KH Wikia