Terra-Xehanort

Terra-Xehanort, also referred to as Xehanort, Ansem, and Not-Ansem, is the result of Master Xehanort forcing his heart into the body of Terra. He is the human form of Ansem and Xemnas.

Kingdom Hearts Birth by Sleep
Terra-Xehanort is created in the Keyblade Graveyard when Master Xehanort uses his Keyblade to unlock his heart and possess Terra's body after the χ-blade is forged. Terra-Xehanort is forced to battle the Lingering Will, Terra's discarded Keyblade Armor that has come to life through Terra's mind, and he is knocked unconscious. The destruction of the χ-blade at the hands of Ventus and Aqua sends Terra-Xehanort to the Radiant Garden.

In the Radiant Garden, Terra-Xehanort battles Aqua, who has been led to him by Terra's voice. Terra-Xehanort is confused about his identity as a result of the battle transpiring within him between Terra's heart and the heart of Master Xehanort; it is when Terra's heart starts to gain the upper hand in this internal struggle that Terra-Xehanort uses Master Xehanort's Keyblade to rid himself of Terra's influence. Terra-Xehanort falls into the Realm of Darkness, along with a "shadowy other", but Aqua sacrifices her Keyblade Armor and Keyblade to rescue him.

Following these events, Terra-Xehanort is discovered by Braig, who takes Dilan and their master, Ansem the Wise, to the young man's location. Possessing no memories whatsoever, save for the name "Xehanort," Terra-Xehanort is taken back to Ansem's castle

Some time later, Braig attempts to start a conversation with Xehanort, only to realize that the man's amnesia appears to be genuine. Despite this, Braig promises to look after Xehanort from then on.

Between Kingdom Hearts Birth by Sleep and Kingdom Hearts
Over the following year, Xehanort became Ansem's foremost apprentice. Eventually, Ansem begun to worry about the darkness that lingers within the hearts of others and seeks a way to stop it before it consumes his people. Ansem constructed a laboratory under his castle where he, Xehanort, and Ansem's five other assistants (Braig, Dilan, Even, Aeleus, and Ienzo) conducted experiments on darkness.

Xehanort, who Ansem had by now come to fully trust as an apprentice and friend, offered to use himself in the experiments. Ansem agreed, also hoping to unlock Xehanort's memories in addition to uncovering a way to repress the darkness within hearts. Xehanort, however, had other plans in mind and decided to conduct his own experiments to go deeper into the research.

Xehanort, Braig, Dilan, Even, Aeleus, and Ienzo carried out their own experiments where they abducted countless people and locked them within the depths of the laboratory where Xehanort conducted horrible experiments on the subjects. After using many test subjects, one set of experiments led to the collapse of their hearts. The subjects then went into unrecoverable conditions and were locked up in the dungeon of the castle. Eventually, Xehanort checked on the subjects and saw that they have transformed into creatures of darkness, which he named "The Heartless" as they apparently lack hearts. At this point, Xehanort had taken Ansem the Wise's name as his own and wrote his own report under this stolen name.

Xehanort then presented the Heartless with living and non-living samples; the Heartless only respond to the living. Xehanort witnessed the Heartless consume living creatures and then multiply into more Heartless. Xehanort deduced that the Heartless seek the hearts of other things, which explained why they only react to living samples, in order to create more of their kind. Xehanort and his associates soon begun to slowly accept the darkness, allowing them to have limited control over the Heartless.

As a result, they also begun to look less and less human, a factor that Ansem himself realized. When Ansem learned that his apprentices have continued with the research without his permission, he called them together and ordered them to cease their efforts immediately, all the while questioning what is happening to his loyal apprentices. Xehanort, however, saw his master as a fool with no understanding of research and secretly kept the research operating.

After observing the behavior of the Heartless and their responses to living things, Xehanort took one aside and observed its behavior. The Heartless begun to move throughout the castle until a door appears, which Xehanort somehow managed to open. Behind the door was a humongous mass of energy, to which the Heartless react immensely. The opening of this door led to the collapse of the world's boundaries, seen in the form of a meteor shower. Xehanort eventually deduced that the door actually leads to the heart of that world and that the opening of this door has led to the collapse of the walls between worlds.

This allowed inter-dimensional travel, and eventually a visitor named King Mickey Mouse arrived, having constructed a Gummi Ship, a spacecraft capable of breaking through world boundaries, out of materials from the meteors and used it to visit many different places in search of answers of recent events. Xehanort and Mickey met and had huge discussions, in which Xehanort, once again, learned of the Keyblade, a weapon that Mickey also possesses.

Xehanort also heard legends about the seven princesses with pure hearts and how they have a connection to the Keyblade. The Keyblade can also be wielded by many, as long as their hearts qualify, and it seems there is a legend of one Keyblade bearer who went on a journey of destiny to seal off the doors to other worlds. Since this is not in Xehanort's interest, he sought a way to find this weapon (which is ironic, given that his former self once wielded one, but was now lost). Mickey befriended Ansem the Wise and the two of them exchanged theories and ideas in his office about what the Heartless could be after. Ansem decided to resist the urge to test their theories while expressing deep remorse for his actions, unaware that Xehanort has gone further than he himself even dared. Xehanort entered the office during their discussion, asking Ansem's permission to test an experiment. Ansem forbid Xehanort to conduct it and told him to forget everything he learned from the research.

This, however, did not deter Xehanort, who proceeded with the experiments and created a machine that creates artificial Heartless, all of which are marked with an emblem created by Xehanort in order to differentiate them from the pure-blood Heartless. King Mickey suspected something odd about Xehanort and warned Ansem to check his lab, collect all his data, and see if everything was under control.

Ansem did so and finally learned the full extent of Xehanort's treachery. Ansem ordered his apprentices to seal off the laboratory and cease their scheme for knowledge. The order is followed, but Xehanort eventually banished Ansem to the Realm of Darkness and ravaged the world with Heartless. The Heartless, under the command of Xehanort, begun spreading to other worlds and destroying numerous ones in their mad search for hearts. One side effect of the destruction of so many worlds is the creation of Traverse Town, made up of the remains of the ruined worlds and populated by the few survivors of those said worlds.

Around this time, Xehanort restored the Master Control Program and Sark to the Hollow Bastion OS. He also abducted Kairi, a resident of Radiant Garden, and sent her out into the Sea of the Skies. He believed that she possess a connection to the Keybearer that would lead her to him, due to her having the signs of a Princess of Heart, in the hopes that he would be able to follow her and prevent the Keybearer from sealing the doors to other worlds.

Xehanort made the final pages of his report, which outline his intentions as well as those of the Heartless. The Heartless seek to consume the hearts of all living things. However, they not only seek human hearts, but the hearts of the worlds themselves. Their ultimate goal is to collect enough hearts to form the biggest heart of all, the heart in which all that exist are evolved from: Kingdom Hearts. Xehanort decided to use the Heartless' instincts to make his own plans: like Master Xehanort before him, to find Kingdom Hearts in order to gain ultimate power, control, and knowledge. Xehanort also learned that the creation of a Heartless can also lead to the creation of another creature called a Nobody, beings that are left over bodies of those whose hearts have been stolen away. They transform into an inhuman state and do not truly exist as they lack a heart to make them truly live.

Xehanort and the others gave themselves to the darkness to gain the ability to control all Heartless and wield the powers of darkness. They lose their hearts in the process and became powerful Nobodies. However, Xehanort is the only apprentice to have both a human Heartless and a human Nobody, both possessing the memories and personality traits prior to their creations. Since they possessed strong hearts and wills, Xehanort and the others were able to retain their human forms as Nobodies. Radiant Garden was almost completely destroyed, saved for the castle and the mutated waterways, which had several modifications done to it by Xehanort and the other apprentices, and most of its people were wiped out while some (like Leon, Aerith, Yuffie, Cid, and Merlin) managed to escape to places like Traverse Town.

Kingdom Hearts II
Sora finds a painting of Xehanort while investigating Ansem the Wise's study. At first, he believes that Xehanort is Ansem the Wise, given that he is the original being of "Ansem", but following discussions with Tron and King Mickey, Sora finally realises the truth about Ansem and Xehanort, and seethes with fury at Xehanort's painting, labelling him as the cause of all the chaos and mostly Riku and Kairi's situation.

Xehanort himself appears in King Mickey's flashback, where Xehanort requests permission to proceed with an experiment but is denied by Ansem, a scenario which Mickey witnessed ten years ago. This memory is what leads Mickey to remember Xehanort's name and identify Xemnas, the leader of Organization XIII, as Xehanort's Nobody.

Kingdom Hearts 3D: Dream Drop Distance
In a flashback, Xehanort is confronted by Braig in the computer room of Hollow Bastion about the unconscious bodies of Even and Ienzo. Xehanort responds by summoning his old Keyblade, and as Braig begins to question as to whether Xehanort's memories have returned or if he never lost them in the first place, Xehanort stabs him in the chest, unlocking his heart. As Braig loses consciousness, Xehanort tells him, "My name is Ansem".

Following the restoration of Master Xehanort due to the destruction of Ansem and Xemnas, Terra-Xehanort is still missing, but Master Xehanort claims that Terra still belongs to him.

Personality
Upon his "birth" in Kingdom Hearts Birth by Sleep, Terra-Xehanort appears to retain Master Xehanort's personality, including his knowledge of Darkness, thus being a mere younger incarnation of the elderly Keyblade Master. The only difference is the occasional interference by Terra, shown when Terra-Xehanort briefly asks Aqua who he is, and when he is briefly forced to stand still during the subsequent fight with her.

Shortly after Terra-Xehanort is defeated by the Lingering Will, and loses some of his memories, he ends up in Radiant Garden, and begins to question his existence upon meeting Aqua - by strangling her. By the time he is found by Braig, Dilan, and Ansem, he has lost all of his memories entirely—except for the name "Xehanort", although at one point, Braig insinuates that the amnesia is a mere ruse.

As one of Ansem's apprentices, Xehanort appears to have had a very professional and no-nonsense attitude, shown by his determination in his studies. He appeared to be easily annoyed by Braig and was shown to be equally as interested in the darkness of hearts as his original incarnation. Xehanort appeared frustrated when Ansem forbade him from continuing his studies and experiments, and ultimately disobeyed his master. When speaking to Xemnas, Ansem the Wise refers to Xehanort as "foolish" and that any world of his "would be an empire of ignorance".

Appearance
Terra-Xehanort's appearance is identical to Terra's, only with silver hair, darker skin and yellow eyes. He also bears a striking resemblance to Master Xehanort in his youth, and some of his physical traits are later carried on to Ansem and Xemnas.

As an apprentice under Ansem the Wise, Xehanort wears a white labcoat with rather loose sleeves that is partway zipped down. The coat also has pockets roughly where Xehanort's hips are. He wears black boots that are identical to those worn by Ansem, Xemnas, and the members of Organization XIII, with a white/silver lining along the top and an indentation on the sides. Underneath his coat, Xehanort wears a grey vest overtop a white collar shirt, along with a purple ascot around his neck. During this time, his hair is worn long, with two bangs framing his face. His eyes have gone from yellow to brown. His hair also sports three backward-facing spikes, one at the top of his head, and one on either side, just above his ears.

Powers, attacks and magic
As a fusion of Terra and Master Xehanort, Terra-Xehanort is able to use many of these Keyblade wielders' abilities. Terra-Xehanort uses Master Xehanort's Keyblade to perform techniques like Ars Solum, a fast combo comprised of multiple hits. He can use Meteor and Quake as well, and he is one of the few bosses that is able to heal with Curaga. When in desperate need of power, Terra-Xehanort gains access to the Dark Impulse Command Style, as well as the Dark Volley and Ultima Cannon Shotlocks.

Terra-Xehanort also can call upon his "Guardian," a Pureblood Heartless-like symbiote that floats behind him and serves as both his main source of offense and defense. It has great power; the Guardian attacks Terra-Xehanort's enemies with physical blows and dark energy projectiles. It can also possess them. Terra-Xehanort's Heartless, Ansem, inherits the ability to summon the Guardian, whose first appearance in story chronology is during Terra-Xehanort's battle against Aqua Kingdom Hearts Birth by Sleep.

Weapon
Terra-Xehanort wields Master Xehanort's Keyblade; the weapon has a spiky shaft, as well as a gleaming eye of darkness near its teeth, which give the Keyblade a battle ax-like appearance. Master Xehanort's Keyblade is black and silver in coloration; it is able to unlock hearts and appears in its wielder's hand in a flash of dark energy. Another eye of darkness appears on the Keyblade's keychain; Terra-Xehanort uses this Keyblade to perform long, powerful combos, as well as several desperation attacks. When Terra-Xehanort loses his memories, he also loses his ability to wield Master Xehanort's Keyblade. A year later, however, he regains the weapon and uses it to unlock Braig's heart.

Trivia

 * Terra-Xehanort does not serve as a boss battle until the series' sixth installment, Kingdom Hearts Birth by Sleep. Until then, he was simply called "Xehanort" and was portrayed as the main antagonist of the Xehanort Saga, although Master Xehanort ended up taking that role instead.
 * Terra-Xehanort's first sentences after being created mirror the speech Ansem gave to Sora when the boy confronted him at the End of the World in Kingdom Hearts.