Master Xehanort

"Darkness cannot be destroyed, it can only be channeled."

- Master Xehanort to Terra

Master Xehanort is the main antagonist of the "Dark Seeker Saga" of the Kingdom Hearts series, and he can be considered as the true primary antagonist of the whole series. He is the original incarnation of Xehanort from which Ansem, the Seeker of Darkness, Xemnas and all others spawned from. He manipulated almost every event in the series, and devised many back-up plans that involve dividing his heart among 13 different beings created from his power and take over the universe.

History
Xehanort was born in Destiny Islands, feeling his home was a prison. But due to an encounter of a future incarnation of himself, Xehanort's destiny was set in stone as he acted on his future self's will before losing his memory and leave the islands to become an apprentice under a Keyblade Master alongside a fellow apprentice named Eraqus. When the two became Keyblade Masters, Eraqus was made steward of the Land of Departure so Xehanort can freely travel the worlds. However, over years of research and travel, Xehanort became obsessed with the events of the Keyblade War. He felt that there was no balance between the light and the darkness, so he planned to recreate the X-Blade to cause a second Keyblade War with hopes to establish balance. By the time he confided his goals to Eraqus, Xehanort had mastered the powers of darkness and used them to scar his former friend in defense.

He attempted to use the darkness of a Keyblade Wielder named Ventus to recreate the X-Blade and serve as a host for his heart to prolong his life long enough for his plan to come to fruition. However, Ventus refused to succumb to his darkness and Xehanort is forced to extract the darkness and create Vanitas before leaving a weakened Ven to die on the Destiny Islands. But seeing the boy pulling through, Xehanort has Ven sent to train Eraqus so he can become Vanitas' equal in order for their reunion to recreate the X-Blade. By that time, Xehanort found a more ideal host in one of Eraqus' two students: Terra.

Birth by Sleep and after
While Vanitas traveled the worlds spreading the Unversed to prepare Ventus for their reunion, Xehanort was looking for the Princesses of Heart (seven princesses with hearts of pure light). He managed to find one, Princess Aurora. It was also at that time, he arranged for Maleficent to find the other Princesses of Heart for him. He also came to Radiant Garden to employ the services of Braig, offering him a Keyblade of his own in return for helping him in getting Terra to embrace his darkness. Though Braig was scarred as a result of Terra using his darkness, winning the youth's trust as a result, Xehanort threateningly claimed him down before infusing part of his heart into Braig's body. But tricking Terra into defeat Eraqus, Xehanort kills his old friend and casts the entire Land of Departure into darkness before telling Terra to meet him in the Keyblade Graveyard where his plan will be completed.

Managing to separate Terra from the others, with Braig holding them off, Xehanort sends Vanitas to enact his reunion with Ven. Managing to get Terra to unleash his full fury on him before seeing the light marking the restoration of the X-Blade, Xehanort uses his Keyblade to transfer his heart into Terra's body, turning the youth into his vessel Terra-Xehanort. However, with a new younger body, Xehanort found resistance from Terra through both his Lingering Will and the heart of Terra itself as he attempts to aid Aqua. It was only when Terra-Xehanort attempted to purge Terra's heart that the vessel loses all his memories except the name "Xehanort" which he took.

However, unable to fully rid himself of Terra, Xehanort reveals the series of back-up plans he arranged that were ultimately carried by Terra-Xehanort's splinter selves, false Ansem and Xemnas. Even though Sora and his friends foil their schemes, Xehanort had another plan set into motion.

Signs of What's Next
After the defeat of Ansem and Xemnas, Yen Sid explains to King Mickey that those actions actually freed Xehanort's heart from the Heartless Ansem and vanquished Terra-Xehanort's left over body which had become his Nobody Xemnas, thus both halves' destruction have now lead to the reconstruction of Xehanort's pure and original incarnation: Master Xehanort.

Dream Drop Distance
Having expecting it, Xehanort arranged for his past self to gather every incarnation or vessel of himself together at the World That Never Was to witness Master Xehanort's return while capturing Sora as he and Riku were in the dream worlds. Eventually, ten Xehanorts, which included his Heartless and Nobody as well as Braig and Isa, were gathered.

When Riku arrives to rescue Sora, who is in the Organization's clutches, King Mickey freezes time to allow Riku to escape. However, Master Xehanort's soul possesses his younger self and duels Riku.

After the battle, Master Xehanort finally revives. Xehanort callously admits he misjudged the X-Blade being recreated with only Ventus and Vanitas, stating that their fate, along with Aqua and Terra's, was all predestined. He further elaborates that his Thirteen Seekers of Darkness, the true Organization XIII, with be able to recreate the X-Blade by clashing with seven lights, the seven wielders of the Keyblade. Though Xehanort attempts to add Sora to his rank to complete the member, Lea's interference ruins it as he and his followers scatter but promises that the final battle will come soon.

Trivia

 * In the English version, he was voiced by the late Leonard Nimoy, who also portrayed Spock in Star Trek and voiced Galvatron in Transformers: The Movie & Sentinel Prime in Transformers: Dark of the Moon. In fact, Nomura cast Nimoy as Xehanort in order to pit Star Trek against Star Wars, with Mark Hamill of Star Wars fame voicing Xehanort's rival Eraqus. In the Japanese version, he is voiced by the late Chikao Otsuka, who also voiced Dr. Eggman and Piedmon.
 * It is currently unknown who will voice Xehanort in both the English and Japanese versions of Kingdom Hearts III or if the English voice acting has finished.
 * Keith Shadis, the drill sergeant from the anime Attack on Titan, almost bears a striking resemblance to Master Xehanort.
 * According to Nomura, Kingdom Hearts III will be the last game where Xehanort is the villain.
 * Master Xehanort is the overarching and most recurring antagonist in the series, as every incarnation is the main antagonist in each game: Xehanort himself is the main antagonist in Birth by Sleep. Ansem, Seeker of Darkness is his Heartless, and he is the main antagonist in Kingdom Hearts. Xemnas is his host body's Nobody and the main antagonist in Kingdom Hearts II. Young Xehanort is his teenage self and the central antagonist in Dream Drop Distance. Master Xehanort is set to be the main antagonist in the upcoming Kingdom Hearts III.