Who is xemnas in Kingdom Hearts

Xemnas does not exist in Kingdom Hearts 1, but he is the leader of Organization 13 because of Ansem in Kingodm Hearts 1. Xemnas is a nobody so there for he does not exist without someone to live by that was once part of the darkness. Therefore when Riku became part of Ansem in the Darkness Xemnas was born a nobody. Also when Sora became a shadow to save Kairi's heart Roxas was born therefore the keybearer for Organization 13.