Terra-Xehanort

Ansem's Apprentice
Xehanort was found in the paradise world of Radiant Garden by Ansem the Wise, a respected sage and the ruler of the world. Xehanort possessed no memory of his life before this, and was greatly injured, but it is mentioned that he appeared when a Great Keyblade War ended. Ansem took Xehanort in and he became Ansem's foremost apprentice. Although he was confused about his past, Xehanort learned greatly and became quite cunning. Xehanort was described by Ansem as having abilities so remarkable that they could be considered supernatural.

Eventually, Ansem began to worry about the darkness that lingers within the hearts of others and sought a way to stop it before it consumed his people. Ansem constructed a laboratory under his castle where he, Xehanort, and Ansem's five other assistants (Braig, Dilan, Even, Aeleus, and Ienzo) would conduct experiments on darkness. Xehanort, who Ansem now fully trusts as an apprentice and friend, offered to use himself in the experiments. Ansem also hoped to unlock Xehanort's memories in addition to uncovering a way to repress the darkness within hearts. Xehanort had other plans in mind though and decided to conduct his own experiments to go deeper into the research.

The Heartless
Xehanort and the other five apprentices began to carry out their own experiments. They abducted countless people and locked them within the depths of the laboratory where Xehanort then 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 transformed into creatures of darkness, which he named "The Heartless" as they lacked 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 responded to the living. Xehanort witnessed the Heartless consume the living creatures and then multiply into more Heartless. Xehanort deduced that the Heartless seek the hearts of other things, which explains why they only react to living samples, in order to create more of their kind. Xehanort and his associates soon began to slowly accept the darkness, allowing them to have limited control over the Heartless. They in turn began to look less and less humane, a factor that Ansem himself realized. When Ansem learned that his apprentices continued with the research, he called them together and ordered for them to cease their efforts immediately, all the while questioning what was happening to his loyal apprentices. Xehanort however saw his master as a fool who had no understanding of research and kept the research operating.

After observing the behavior of the Heartless and their responses to living things, Xehanort took one of the Heartless aside and observed its behavior. The Heartless began to move throughout the castle until a door appeared which Xehanort was somehow able to open. Behind the door was a humongous mass of energy to which the Heartless reacted immensely. The opening of this door led to the collapse of the world's boundaries, which was seen in the form of a meteor shower. Xehanort eventually deduced that the door actually led to the heart of that world and that the opening of this door led to the collapse of the walls between worlds. This allowed inter-dimensional travel as all the walls between worlds were now broken and eventually a visitor showed up named King Mickey. He had 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 learned of the Keyblade, a mysterious weapon that Mickey himself possessed.

There were also legends that told of seven princesses with pure hearts and how they have a connection to this 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 was not in Xehanort's interest, he sought a way to find this weapon. Mickey eventually met and befriended Ansem the Wise and the two of them exchanged theories and ideas in his office about what the Heartless were after. Ansem decided to resist the urge to test their theories while expressing deep remorse for his actions. However, Ansem had no idea that Xehanort had gone further than he himself even dared. Xehanort entered the office during their discussion, asking Ansem's permission to test an experiment. Ansem forbade Xehanort to conduct it and told him to forget everything he learned from the research.

Even though Ansem had no further urge to research the darkness, the experiments led by Xehanort continued including the creation of a machine that created artificial Heartless, all of which were marked with an emblem created by Xehanort in order to differentiate them from the pure-bred Heartless. King Mickey suspected something odd about Xehanort and told Ansem to check his lab, collect all his data, and see if everything was under control. Ansem did so and learned that Xehanort had taken his name as his own and wrote a detailed report. From the report, Ansem learned of the horrible torture inflicted on people by the inhumane experiments that Xehanort had done. Ansem ordered his apprentices to seal off the laboratory and cease their scheme for knowledge.

The Path to Destruction and Knowledge
Ansem's apprentices did as he instructed them but Xehanort eventually banished Ansem to the Realm of Nothingness and ravaged the world with Heartless. The Heartless under the command of Xehanort began spreading to other worlds and destroyed numerous ones in their mad search for hearts. One side effect of the destruction of so many worlds was the creation of Traverse Town, made up of the remains of the ruined worlds and populated by the few survivors of those said worlds. Xehanort then ordered for the seal on the laboratory to be broken and that a room that he called the "Room of Sleep" be constructed. Once done, Xehanort often went in and spoke as if there was someone else in the room. It is later revealed that the room housed the armor of a fallen Keyblade wielder although it is not known what the purpose of this was. Xehanort then abducted and sent Kairi, a resident of Radiant Garden, to the oceans of other worlds. The reason for this was because Xehanort thought Kairi had a connection to the Keyblade bearer, as she seemed to possess power comparable to that of a Princess of Heart, which is rumored to posses a connection to the Keyblade. He hoped to use her to find the Keyblade master and prevent him from sealing off the doors to other worlds.

Xehanort made the final pages of his report, which outlined 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. He would 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 eventually gave themselves to the darkness to gain the ability to control all Heartless and wield the powers of darkness. They lost their hearts in the process and they became powerful Nobodies. However, Xehanort was the only one to have both a human Nobody and Heartless, both possessing the memories prior to their creations. Since they possessed strong hearts, Xehanort and his followers were able to retain their human forms as Nobodies. Radiant Garden was almost completely destroyed, save 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 managed to escape to Traverse Town, such as Leon, Aerith, Yuffie, Cid and Merlin.

A Heartless and Nobody
Xehanort's Nobody took the concept of his original name being an anagram with an X in it and applied it to the name he stole, Ansem. Thus he was called Xemnas who created The Organization, later called Organization XIII, with the other apprentices at its core. Like Xemnas, all the other members rearranged their names and put an X in them in order create a new identity for themselves. They sought to become complete beings again and be whole. Meanwhile, Xehanort's Heartless, still calling himself "Ansem", remained a spirit seeking to plunge all that is in darkness. Both portions of Xehanort sought Kingdom Hearts in order to wield the power it possesses and unleash it into the universe.

Xehanort's Heartless' plans were to control other beings and use them to collect the Princesses of Heart and use them to open up the portal to Kingdom Hearts. To this end, he commanded the Heartless to manipulate the darkness within the Disney villains to serve their needs. Maleficent, being manipulated by the Heartless, led this group of villains to control the darkness by using the heartless and collecting the princesses to open the path to Kingdom Hearts through an artificial keyhole. This group used Hollow Bastion as a base of operations and used Ansem's reports to help them control the heartless and the darkness. None of them knew, however, that they were being used by a far greater evil that was residing in the shadows, waiting for the opportune moment to claim Kingdom Hearts for himself. At the same time, Xehanort's heartless would use the Heartless to destroy entire worlds and collect the world hearts to form the dimension of Kingdom Hearts itself. He also searched for a host to take control of so that he may regain a physical presence. His choice for a host would later turn out to be Riku. Exploiting Riku's jealous friendship with Sora, Xehanort's heartless nearly shattered their friendship and took possession of Riku's body, sending his heart to the dark realm. Unfortunately for him, the goal he sought for throughout his whole life, Kingdom Hearts, ended up destroying him with its light, giving Riku back his body. Kingdom Hearts was soon sealed away by Sora and King Mickey, which destroyed billions of heartless and the End of the World as well as restoring all the worlds taken by Xehanort and the Heartless. (Xehanort's Heartless would still live on in Riku)Meanwhile, Xemnas, the Nobody of Xehanort, sought to find Kingdom Hearts by collecting human hearts. His goal was to use Kingdom Hearts to make himself a kingdom, where he would be the ruler forever. Leading Organization XIII (Xigbar, Xaldin, Vexen, Lexaeus, Zexion, Saïx, Axel, Demyx, Luxord, Marluxia, Larxene, Roxas, and Xion), Xemnas controlled all Nobodies and constructed a fortress that would serve as a base of operations: The Castle that Never Was. Organization XIII recruited other powerful Nobodies in their plans to find Kingdom Hearts and use its power to become complete beings again. Xemnas eventually found a fortress known as Castle Oblivion and converted it into a base of experiments where the nature of memory would be experimented on. He was also searching frantically for a room called the "Room of Awakening" and believed it to be somewhere within this fortress. In the meantime, Organization XIII brought chaos and destruction to many worlds in order to create more Heartless and Nobodies to control. Research was also put into the Keyblade and the Organization eventually learned that it held the literal key to forming and obtaining Kingdom Hearts. And Xemnas, unlike his Heartless counterpart, achieved his goal. But after all of the other Organization members were slain by Sora, fate turned back on him and Kingdom Hearts was scattered by Ansem the Wise himself in an explosion that killed the former ruler of Radiant Garden. Xemnas, with no other option, absorbed the remnants of Kingdom Hearts and became ultimately. However, in a climactic battle with Sora and Riku, Xemnas was destroyed by the light of the Keyblade and faded, taking Kingdom Hearts with him. This also ended the reign of Organization XIII and the nobodies and, as Sora stated after the battle, restored the realm of light to peace and safety.

By the end of Kingdom Hearts II, the madness of Xehanort seemed to have finally been destroyed by Sora, Riku, Kairi, and Roxas, but it is unknown if this can truly be seen as a fact.