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 X-Blade, a legendary Keyblade capable of unlocking Kingdom Hearts.

Unfortunately the process left Ven in a comatose-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. But Ventus was still far too weak in comparison to Vanitas, for the two needed to be equal in power for the creation of the X-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 Master Qualification Exam taken by Terra and Aqua 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 disappears 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. Working 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. Lying that Vanitas is responsible for the whole chaos, Master Xehanort forms a pact with Terra to destroy him and takes Terra under his wing, 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.

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 X-Blade and unlock Kingdom Hearts. In the ensuing battle, Master Xehanort freezes Ventus and has Vanitas knock Aqua out cold, 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
In Blank Points, it is shown that the hearts of Master Xehanort and Terra are (at the time) battling over internal dominance within the new Xehanort.

Appearance
Master Xehanort appears to be an old man, bald except for thin eyebrows and a curled, silver goatee. His ears are pointed and his eyes are yellow. He has broad, hunched shoulders and a crooked back. He overall appears as a somewhat feeble old man, certainly deceiving given his absolute power.

His attire is nearly identical to the clothes that Ansem, Seeker of Darkness wears, namely, a white and black cloak with a red inner lining, a white shirt, black boots and white gloves. The only major difference in appearance between them is that Ansem has his chest bared, along with his emblem on the front, while Master Xehanort does not. There are a few minor changes as well - Ansem's cloak has a gold lining on the edges, while Master Xehanort's cloak has black ones. This is later carried on to Ansem, explained because this particular Heartless was made from the heart of Master Xehanort.

Master Xehanort's previous attire is briefly shown as a Black Coat, possibly as a predecessor to the attire of Organization XIII.

Master Xehanort is briefly shown when he was younger (though his face is never shown), he's seen with fairly long, mildly tanned skin, and silver hair with an interesting hairstyle (similar to the hairstyles of Terra, Xehanort, Ansem, and Xemnas). He also wears a sleeveless black shirt and pants of the same color.

Personality
Much like Xehanort, "Ansem", and Xemnas, Master Xehanort is shown to be a cunning, callous, and pragmatic being with the sole goal of merging with Kingdom Hearts, the lives of innocent people and even his closest friends meaning absolutely nothing to him. To this end, he is willing to put whatever he pleases on the line or destroy anything in his way, demonstrated when he manipulated several characters such as Terra, Aqua, Ventus, Braig, and even Maleficent; creates Vanitas, a sentient being for the sole purpose of forwarding his evil plan; and slays his old friend, Master Eraqus, in cold blood after tricking Terra into defeating him in battle.

His personality, at times, contradicts itself. His past shows that he was once a noble man who willingly took Ventus as his apprentice and cared for him until he started to lose his grip on sanity. Even after this, he still shows pity for Ventus and leaves him under Master Eraqus's care, and at a later time, even expresses genuine joy in one of his reports when Eraqus personally asked him to oversee the Master Qualification Exam. At the end of the game, however, he appears to have put most of his good points behind him, shown when he stabs his old friend Eraqus in the back, and with his cold-hearted manipulations.

Overall, Master Xehanort is arguably the catalyst of all the events in the series so far, and could even be seen as the true villain of the Xehanort Saga. He shares most of his personality traits with Xehanort (before the latter's fight against the Lingering Sentiment and Aqua) and "Ansem", while Xemnas appears to be influenced several times by Terra's characteristics. He has a few unusual tendencies and quirks, however, such as turning away from the people he speaks to, or over-dramatizing his hand gestures when delivering a speech.

Abilities
His age often causing opponents to underestimate him, Master Xehanort is a skilled Keyblade master and magic user. Able to teleport if he is in danger, Master Xehanort strikes opponents with powerful, fast-paced combos. He also can bombard foes with Thunder, Blizzard, and Earth-based magic.

Master Xehanort shows a great deal of skill in utilizing the heart and its capabilities, able to create a living being, Vanitas, out of the darkness of Ventus's heart when he unlocks it and even able to direct his heart into Terra's body to possess it after his defeat in the Keyblade Graveyard.

Once he becomes the young man known as Xehanort through the possession of Terra's body, Master Xehanort proves to be the stronger of the two hearts residing within him. Master Xehanort's overpowering Terra's is demonstrated several times during the battle between Terra-Xehanort and Aqua, Master Xehanort's influence beginning the fight in the first place and even releasing Terra's heart from within the body of his younger incarnation when Terra begins to regain control.

Weapon
Master Xehanort is able to wield his Keyblade with great professionalism despite his age, and enough of his strength has remained over the years that he is able to use it in fast-paced physical combos. His battle pose is similar to that of both Vanitas and Riku, but he mainly allows the Keyblade to hang loosely at his side as he walks slowly towards opponents. Master Xehanort also uses his Keyblade to unlock countless hearts, including his own.

When Master Xehanort possesses Terra's body to become Terra-Xehanort, he abandons Terra's Keyblade and replaces it with his own. Terra-Xehanort wields the weapon with great skill, combining several of Terra and Master Xehanort's abilities to form his own deadly combos. As this Keyblade was gained by Terra-Xehanort through Master Xehanort's heart's more powerful influence, it is also used through Master Xehanort's influence to unlock Terra-Xehanort's heart.

Trivia

 * Tetsuya Nomura stated the relationship between Master Xehanort and Master Eraqus is something like old classmates.
 * In the English version of Kingdom Hearts Birth by Sleep, Master Xehanort is voiced by Leonard Nimoy, who was chosen by Tetsuya Nomura specifically for his role as Spock in the Star Trek franchise, and who announced his retirement from acting shortly after portraying Master Xehanort.
 * Master Xehanort is voiced by Chikao Ohtsuka in the Japanese version of Kingdom Hearts Birth by Sleep, the real-life father of Akio Ohtsuka, the Japanese voice actor of Xehanort and Ansem (aka Xehanort's Heartless). Chikao Ohtsuka also previously voiced Captain Hook (but was replaced by Naoya Uchida for Kingdom Hearts Birth by Sleep).
 * In Kingdom Hearts Birth by Sleep, Yen Sid wonders if Master Xehanort still has "distracting thoughts". This is a sign that the two have possibly met before, as Yen Sid is revealed to be a former Keyblade Master and an acquaintance of Master Eraqus.
 * Tetsuya Nomura has confirmed in interviews that since "Ansem" and Xemnas were slain in the correct order, Xehanort will return in future installments and that Kingdom Hearts III will feature his final battle against Sora.