Xehanort

Master Xehanort is the original master of Ventus, the creator and master of Vanitas, and the original incarnation of Xehanort. He is a Keyblade Master and the main antagonist of Kingdom Hearts Birth by Sleep.

Kingdom Hearts Birth by Sleep
In his youth, Xehanort, who once lived on a beach, had dreams of leaving his home in search for something greater. At some point he found a way to depart his home world and was trained to be a Keyblade Master, eventually befriending Eraqus, another Keybearer. Throughout his life, Xehanort traveled to many different worlds and obtained vast knowledge concerning Keyblade lore, the power of Light and Darkness, a detailed knowledge of the Heartless, the mysteries of the Keyblade War and Kingdom Hearts. Realizing the power unlocking the "heart of all worlds" would grant, Xehanort set his goal on finding a way to open the door to Kingdom Hearts.

By the time he discovered a way of opening that door, Master Xehanort had grown old, and realized that he must transfer his essence and knowledge to a "new vessel" in order to survive to see his plans reach fruition. To this end, he sought out an apprentice and found the boy Ventus, who he began training as Keyblade wielder, and eventually his vessel. However, Ven was too weak and a poor candidate, so Master Xehanort decided to instead use him as part of his ultimate plan. By using his Keyblade to split Ven's heart and create a being with a heart of pure light and a being with a heart of pure darkness. The being of light remained as Ventus, while the dark being assumed the name "Vanitas". With these two boys, Master Xehanort intended to forge the χ-blade, a legendary Keyblade capable of unlocking Kingdom Hearts.

Unfortunately the process left Ven in a coma-like state with his broken heart of pure light slowly fading out. Master Xehanort (in a black coat) decided to leave Ven to die in a peaceful setting in his old home, the Destiny Islands. To his master's surprise, Ventus's heart somehow survived and Xehanort realized the boy could still be of use. However, Ventus was still far too weak in comparison to Vanitas, for the two needed to be equal in power for the creation of the χ-blade. Xehanort brought his former apprentice to his old friend Master Eraqus to train Ven and make him stronger.

At this point, Master Xehanort set his eyes on one of Master Eraqus's apprentices: Terra, within whom he sensed the correct potential to be his new vessel. While in the Land of Departure, Master Xehanort sabotages the Mark of Mastery Exam taken by Terra and Aqua, causing Terra to fail, and later tells him that if he were to become a true Keyblade Master, he would have to embrace the darkness in his heart rather than fight it. Shortly thereafter, Master Xehanort and Vanitas disappear on an apparent quest to find the Princesses of Heart.

During his travels, Master Xehanort manipulates Master Eraqus's apprentices (Terra, Aqua, and Ventus), who had been sent to find him and destroy the Unversed, a malicious species created as a side-effect of Vanitas's existence. He encounters Terra in the Keyblade Graveyard and puts his manipulative skills to the test, explaing the reason for his actions: He is trying to safeguard the light from the "demon" he unleashed. He then goes on to explain Vanitas's origins, how he was accidentaly created when Master Xehanort tried to save Ventus from succumbing to darkness by removing the darkness from him. Lying that Vanitas is responsible for the whole chaos of the Unversed, Master Xehanort pleads with Terra to help right this wrong by destroying Vanitas.

He next travels to the Radiant Garden and strikes a bargain with Braig (who desires the Keyblade for himself), Master Xehanort stages his own capture and has Braig fight Terra, with Terra succumbing to the darkness and disfiguring Braig's face permanently. Master Xehanort tells Terra that he is a true Keyblade Master as he was able to channel the darkness. He then gives Terra an opportunity to be his pupil, claiming that they can do the worlds much greater good. Master Xehanort then pulls the final string, calling him by the name "Master Terra" and gaining the young man's trust.

Later on, Master Xehanort has Vanitas abduct Mickey Mouse as bait to lure Ventus to the Keyblade Graveyard, where he reveals to him the truth about his past, stating also that Master Eraqus knows about it. While Ven goes to see Eraqus, Xehanort tells Terra that Eraqus has gone mad and is about to destroy Ventus. Terra is tricked into defeating Master Eraqus in battle, allowing Xehanort to callously deliver the finishing blow to his former friend. Master Xehanort then tells Terra to go to the Keyblade Graveyard where he will see Aqua and Ventus for the last time before falling prey to the darkness. He then covers the Land of Departure in darkness, completely destroying the world and leaving nothing but the castle's remains, telling Terra he would not need a home where he is going.

Soon enough Terra, Aqua, and Ventus discover the truth and confront Master Xehanort and Vanitas at the Keyblade Graveyard (the remains of the legendary Keyblade War). There, Master Xehanort reveals to them his true plans to create the χ-blade and unlock Kingdom Hearts. In the ensuing battle, Master Xehanort freezes Ventus and has Vanitas knock Aqua out cold, while gleefully telling Terra that he is powerless to save them, causing Terra to lose control of his anger and succumb again to the darkness in his heart.

Terra uses the power of darkness to defeat the elderly Keyblade master, but Xehanort enacts his final scheme and uses his Keyblade to unlock his own heart and transfer it into Terra's body, prolonging his life and transforming him into the new Xehanort while his original body fades into darkness with a triumphant smile.

Blank Points
The hearts of Master Xehanort and Terra are (at the time) shown disputing over internal dominance within the new Xehanort. Despite Master Xehanort's insistence that he will soon incorporate Terra's heart into his own, Terra remains confident that he will win over Master Xehanort, who realizes that Terra is harboring the heart of Master Eraqus. Despite this, Master Xehanort shows no concern, and reveals to Terra that he has backup plans should his possession of Terra fail.