Xehanort

Master Xehanort is a Keyblade Master and the original incarnation of Xehanort. He serves as the main antagonist of Kingdom Hearts: Birth by Sleep. He is the original master of Ventus, and later the master of Ventus's darkside, Vanitas.

Kingdom Hearts Birth by Sleep
Master Xehanort was once an islander from Destiny Islands, who had a dream of leaving the islands on his own. Years later, he found a way to leave his home world and become a Keyblade warrior, and during his life as a warrior, he befriended another Keybearer named Eraqus, and started training his own apprentice Ventus.

However, as years went by, Xehanort started to change. He became sinister and was determined to figure out the mysteries of the heart. He experimented on Ventus, using the Heartless to hold him down while Xehanort unlocked his heart and created Vanitas, Ventus's darkness incarnate.

Xehanort decided to drop what was left of Ven on his old home, Destiny Islands. However, Ven still seemed to have a consciousness, summoning his Keyblade in his sleep. Xehanort felt pity for his former apprentice, so he left Ven in the hands of his old friend, Eraqus, to train Ven and make him into a Keyblade Master. During this time, Master Xehanort's lust for power reached its pinnacle when he learned of the ability that Ventus and Vanitas had to create the X-Blade, a legendary Keyblade with the power to open Kingdom Hearts. But old and frail as he was, Master Xehanort knew his time was running out, so he set his eyes on another Keyblade apprentice: Terra, within whom he sensed the correct potential. To this end, he sabotaged the Master Qualification Exam taken by Terra and Aqua by augmenting the darkness in Terra's heart (in secret), and later told him that if he were to become a true Keyblade Master, he would have to embrace the darkness rather than fight it. Shortly thereafter, Master Xehanort and Vanitas disappeared, on an apparent quest to find the Princesses of Heart.

During his travels, Master Xehanort manipulated 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. Master Xehanort staged his own capture and had Braig fight Terra, with Terra succumbing to the darkness and disfiguring Braig's face permanently. Lying that Vanitas was responsible for the chaos, Master Xehanort formed a pact with Terra to destroy him. Later on, Master Xehanort confronted Ventus and revealed to him the truth about his past, stating also that Master Eraqus knew about it, and at the same time informed Terra that Eraqus had gone mad and sought to destroy Ventus. As expected, Terra defeated Eraqus in battle, and Master Xehanort callously delivered the finishing blow to his former friend.

Soon enough, Terra, Aqua, and Ventus discovered the truth, and confronted Master Xehanort and Vanitas at the Keyblade Graveyard (the remains of the legendary Keyblade War) where Master Xehanort revealed 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 reach fruition. In the ensuing battle, Master Xehanort froze Ventus and had Vanitas knock Aqua out cold, causing Terra to lose control and succumb to the darkness. Master Xehanort was defeated by Terra, but used his Keyblade to unlock his own heart and transfer it into Terra's body, transforming him into the new younger Xehanort. Master Xehanort's original body faded into darkness with a triumphant smile.

In the one of the game's final scenes, it is revealed that Master Xehanort and Terra are battling over internal dominance within the second Xehanort's mind, but with the destruction of both "Ansem" and Xemnas at the hands of Sora and Riku, Master Xehanort's status is currently unknown.

Appearance
Master Xehanort appears to be an old man, bald except for thin eyebrows and a long 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. During Terra's time at Destiny Island when glimpsing at Riku, a younger Xehanort is briefly shown though his face is never revealed. He is seen with fairly long hair that resembles that of Xehanort and Xemnas.

His attire is nearly identical to the clothes that Xehanort's Heartless 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 Xehanort's Heartless has his chest bared, along with his emblem on the front, while Master Xehanort does not. There are a few minor changes as well - Xehanort's Heartless's cloak has a gold lining on the edges, while Master Xehanort's cloak has black ones. This is later carried on to Xehanort's Heartless, explained because this particular Heartless was made from the heart of Master Xehanort.

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 his own Keyblade, which has a black/silver finish, a spiky shaft, a head resembling the blade of a battle axe, and bears some similarities to the Oblivion Keyblade. His Keyblade also has two demonic-like eyes that were previously unique to the Soul Eater, Way to the Dawn, and Vanitas'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 the body of another, displayed when he does this to Terra and takes over him completely, combining his own powers with Terra's powers and creating the ultimate Keyblade Master, Xehanort. It is through the actions of the Lingering Sentiment and Aqua that Master Xehanort loses his memories along with his ability to wield the Keyblade, thus becoming a less dangerous enemy. But still even without the Keyblade, he is a foe not to be underestimated, demonstrated in Xehanort's Heartless and Nobody's numerous battles with Sora.

Personality
Much like Xehanort, "Ansem", and Xemnas, Master Xehanort is shown to be a cunning, callous, and purely evil being with the sole goal of merging with Kingdom Hearts. To this end, he is willing to put whatever he pleases on the line or destroy anything in his way, demonstrated when he manipulates 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.

Master Xehanort is not without good points, however. His past shows that he was once a noble man who willingly took Ventus as an 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 Eraqus's care, although at the end of the game he appears to have put this behind him, shown when he freezes Ventus solid and almost kills him.

Overall, Master Xehanort is arguably the catalyst of all the events in the series, and could even be seen as the true villain of the franchise. He shares most of his personality traits with Xehanort's Heartless, while Xehanort is an amnesiac and Xemnas appears to have more of Terra's characteristics than Master Xehanort's characteristics. For unknown reasons, he has a tendency to turn away from the people he speaks to, shown when he speaks to characters such as Terra, Vanitas, and Eraqus.

Trivia

 * Tetsuya Nomura stated the relationship between Master Xehanort and Master Eraqus is something like old classmates.
 * Master Xehanort is voiced by Chikao Ohtuska, the real-life father of Akio Ohtsuka, the Japanese voice actor of Xehanort and Xehanort's Heartless. Chikao Ohtsuka previously voiced Captain Hook (but was replaced by Naoya Uchida for Kingdom Hearts: Birth by Sleep).
 * Tetsuya Nomura hinted in the Director's Report XIII that Xehanort will return in future instalments, but it is currently unknown if he will return as Xehanort or Master Xehanort.