Who is Xehanort in Kingdom Hearts

Xehanort Xehanort is Ansem's apprentice. Ansem told him thst he was going too far with experiments, but Xehanort didn't listen, soon became a Heartless, and called himself Ansem, even though he's still Xehanort. Sora beated him in the first game, but his Nobody, Xemnas, is stronger. Sora beated Xemnas in the second game as well.