Xehanort

Master Xehanort is a Keyblade Master and the main antagonist of Kingdom Hearts Birth by Sleep. He is the original incarnation of Xehanort, the series' main antagonist.

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 named 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 Ventus and Vanitas' ability to create the X-Blade, a legendary Keyblade with the power to open Kingdom Hearts itself. 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 Terra's Master Qualification Exam 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 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' existence. Joining forces with a man named Braig, 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 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 still battling over dominance inside the mind of the new Xehanort, although it seems that Master Xehanort is the one who will win, but with the destruction of both Xehanort's Heartless, "Ansem", and Nobody, Xemnas at the hands of Sora, 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's Heartless.

His attire is nearly identical to the clothes that Xehanort's Heartless wears in Kingdom Hearts, 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, although it was in Terra's body at the time.

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. 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. 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 that of Terra 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 a foe not to be underestimated, demonstrated in his numerous battles with Sora.

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 in Kingdom Hearts, but was replaced by Naoya Uchida for Kingdom Hearts: Birth by Sleep.
 * Master Xehanort has a tendency to turn away from the people he speaks to, as displayed when he speaks to Terra, Vanitas, and Master Eraqus.