Xehanort

Xehanort was a student of Ansem The Wise and is the main Villain of most Kingdom Hearts games. His name is made from "no heart" and a "X".

Heartless
Xehanort's heartless called himself Ansem and is the final boss of Kingdom Hearts.

Nobody
Xehanort's nobody founded Organization XII and changed his name to Xemnas. "Xemnas" is made from "Ansem" and a "X". He is the final boss in Kingdom Hearts II.