Xehanort 

In the Kingdom Hearts series, he was the first apprentice of Ansem the Wise, having been discovered "on death's door" and afflicted with amnesia when he was young. He was Ansem's first test subject, and carried Ansem's experiments further than advised, even though he and the others were forbidden from any more experimentation and ordered to destroy the results of their past research. He eventually stole Ansem's identity and became a Heartless and a Nobody along with the others. His Nobody is Xemnas, the leader of Organization XIII. His Heartless was known as Ansem, but is simply Xehanort's Heartless.

Sora wasn't very happy to find out that the man he thought was Ansem was really the Heartless of his apprentice, Xehanort.

Xehanort by Syretia December 11, 2008

Young Xehanort 

An antagonist found in the Kingdom Hearts series of video games.

The Xehanort at the point after he inhibits Terra's body, and is found by Ansem the Wise.

Is the main antagonist responsible for rebuilding Organization 13 for vessels more worthy of Xehanort's heart by traveling through time. Featured in the game Kingdom Hearts 3D. Is the final boss in Kingdom Hearts 3D, fought by Sora (And is a total bitch to defeat).

Upon receiving fatal damage, he enters the face of a clock with a massive amount of health, remains static, and sends clones out to deal half of Sora's HP in one combo. Sora must remain mobile at all times, dealing damage little by little until time runs out and you are sent back in time to the previous fight, with Young Xehanort at two and a half bars of health.

Upon taking fatal damage the second time, Young Xehanort enters that same clock face and the process repeats, except the damage on the clock remains.

Extraordinarily difficult to defeat without the abilities Second Chance and Once More, both of which are difficult to obtain through the means of rare spirits.

A tribute to the stereotype of Kingdom Hearts' practically impossible boss fights at higher difficulties

Sora : Alright, half a bar of health left.. I'm almost dead.. If i can just get this one combo off, i'll have killed him and the fight will be over!

Young Xehanort : Time, stop! -enters clock face-

Sora : What?!?

Clone : Rushes at Sora at a million MPH and kills him in one hit

Player : ....

Young Xehanort by An Annoyed KH3D Player December 10, 2013