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, living on a beach, dreams of leaving his home in search for something greater. At some point he finds a way to depart his home world and is trained to be a Keyblade Master, eventually befriending Eraqus, another Keybearer. Throughout his life, Xehanort travels to many different worlds and obtains 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" will grant, Xehanort sets his goal on finding a way to open the door to Kingdom Hearts.

Having become an old man at that point, Master Xehanort realizes he needs "a new vessel" so his knowledge will not be wasted and his goal of obtaining Kingdom Hearts can be realized. To this end he discovers Ventus and begins training him to become a Keyblade wielder. Being too weak and gentle to be his Master's vessel, Master Xehanort instead uses Ven to enact his ultimate plan. By shattering Ven's heart in two to create a heart of pure light (Ventus) and a heart of pure darkness (Vanitas), Master Xehanort intends to forge the X-Blade, a Keyblade capable of unlocking Kingdom Hearts.

Unfortunately the process leaves Ven in a comatose-like state with his broken heart of pure light slowly fading out. Master Xehanort (in a Black Coat) decides 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 survives and Xehanort realizes the boy can still be of use. But Ventus is still far too weak in comparison to Vanitas, for the two need to be equal in power for the creation of the X-Blade. Xehanort brings his former apprentice to his old friend Master Eraqus to train Ven and make him stronger.

At this point, Master Xehanort sets his eyes on one of Master Eraqus's apprentices: Terra, within whom he senses the correct potential to be his new vessel. While at the Land of Departure, Master Xehanort sabotages the Master Qualification Exam taken by Terra and Aqua and later tells him that if he is to become a true Keyblade Master, he will have to embrace the darkness in his heart rather than fight it. Shortly thereafter, Master Xehanort 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 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 as well as his intention to use Terra's body as a vessel to continue his existence long enough to see his plans of obtaining Kingdom Hearts reach fruition. 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.

In one of the game's final scenes, it is revealed that the hearts of Master Xehanort and Terra are (at the time) battling over internal dominance within the new Xehanort. However, with the destruction of both "Ansem" (the Heartless of Xehanort) and Xemnas (the Nobody of Xehanort) at the hands of Sora and Riku, the status of Master Xehanort is currently unknown.

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.

Abilities
Despite his bent and fragile appearance, Master Xehanort seems to be one of the most powerful figures to appear in the Kingdom Hearts universe and also has the ability to wield Master his own Keyblade, which has a black/silver finish, a spiky shaft, a head resembling the blade of a battle axe. His Keyblade also has two demonic-like eyes that were previously unique to the Soul Eater, Way to the Dawn, and his second apprentice's Keyblade.

He is clearly a very powerful mage and possesses exceptional physical strength. With his magical abilities he is able to make massive columns of earth erupt from the ground and has also been shown to be able to lift hundreds of Keyblades from the ground with a powerful manipulation of wind, creating a destructive vortex which moves at his will. His ice magic not only damages on impact, but also spreads through Terra's left arm freezing it in the process. After grabbing Ventus by the head with a single hand and crushing his helmet he instantly froze his entire body although it appears to have been only externally as he was still conscious and moved his eyes.

He also displayed the ability to either teleport or move at an extreme speed as he appeared to have vanished when Ven attempted to slash him from the back. His skill with the Keyblade is also impressive. He deflected Terra's powerful strikes effortlessly and is able to wield it with either hand. He also has an as-of-yet unexplained ability involving the Keyblade where he can turn it into a ball of blue-purple energy that can be fired into the sky and apparently summons Kingdom Hearts.

His greatest and arguably deadliest ability, however, is that of using his Keyblade to transfer his heart into Terra's body and takes over him completely, combining his own powers with Terra's powers and creating Xehanort, although this ability is luckily countered when the new Xehanort loses his memories, including that of wielding the Keyblade.

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.

Fighting Style
Despite being the instigator of the events of Kingdom Hearts Birth By Sleep, Master Xehanort only appears as a boss in Terra's story. Master Xehanort is a skilled warrior with the Keyblade despite his age. He is seen casting several spells and even uses the flying Keyblades to attack.

Quotes

 * "You're fine as you are. Darkness cannot be destroyed, it can only be channeled."
 * "Behold... These lifeless keys used to be full of power, united with the hearts of their masters. On this barren soil, Keyblades of Light and Darkness were locked in combat... As a great Keyblade War raged!"
 * "We know so little about the Keyblade War. It was just the beginning."
 * "He has no control over the darkness in his heart. He's an abomination."
 * "Seek out the darkness that upsets the balance."

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 whom announced his retirement from acting shortly after portraying Master Xehanort.
 * Master Xehanort is voiced by Chikao Ohtsuka, 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, but it is currently unknown if he will return as Xehanort or as Master Xehanort.