Xemnas

"All that and more. I'm carrying on what you yourself began, and I'm creating a brand new world, one heart at a time. I thought you'd praise me, but all you ever do is hold me back. I understand, though. Unlike me, you have a heart. And you're powerless to control it. Consumed, by the jealousy you feel toward the student who surpassed you."

- Xemnas to his former mentor, Ansem the Wise.

Xemnas is the Nobody of Terra-Xehanort who serves as one of the main antagonists (along with Riku) in Kingdom Hearts 358/2 Days and the main antagonist in Kingdom Hearts II. He is the leader of the notorious Organization XIII. He controls the strongest breed of Nobodies, the Sorcerers. He returned in Kingdom Hearts 3D: Dream Drop Distance as one of the supporting antagonists.

Creation

 * See: Master Xehanort and Xehanort

Ansem the Wise started to research the Heartless with an apprentice named Xehanort, who is actually the body of Terra converted into an amnesiac vessel by Master Xehanort. When Ansem decided to stop his research, spurred by the memories of his previous incarnation, Xehanort continued the research with the aid of Braig, Master Xehanort's accomplice, to find a way to manipulate the mind through the heart. While working with his project, using Master Xehanort's Keyblade on Braig and the other apprentices they duped into helping them, Xehanort intentionally separated his heart and body: Creating the Heartless that calls himself "Ansem" and the Nobody Xemnas.

Plan
Xemnas, as one of the rare and strong Nobodies that could think and function like a human, made a plan set up by his previous incarnation. With the aid of Xigbar, the Nobody of Master Xehanort's accomplice Braig, Xemnas gathered the special case Nobodies of the residents of Radiant Garden to join him and Xigbar as the first eight members of Organization XIII: Xaldin, Vexen, Lexaeus, Zexion, Saïx and Axel. From there, his forces recruited Demyx, Luxord, Marluxia, and Larxene while he personally recruits Roxas as their final member. A few days after finding Roxas, Xemnas encountered Sora and used some of the memories he took to have a replica of him created. That replica, Xion, was made an unofficial member of the Organization as both she and Roxas were used to gather hearts to provide Xemnas with his personal Kingdom Hearts.

However, with only Xigbar knowing the truth, Xemnas's goals is to collect 11 "empty vessels" to hold a piece of Master Xehanort's heart, which would be achieved by connecting them to Kingdom Hearts. But the plan fell apart when all the members deployed to Castle Oblivion were defeated with the defection of Xion, Roxas, and Axel half a year later. Regardless, Xemnas continued with the plan as he encouraged Sora to kill as many Heartless as possible before Ansem's interference severely crippled Xemnas's plans.

Battle
In the final battle with Xemnas you have to fight him a total of 4 times.

Part 1 The Test
Before fighting Xemnas as the final boss, he tests Sora in a one on one fight. He has the ability to put an aurora around Sora, so that Sora will take damage until he dies unless you go to the tower in the back and use the reaction commands given. When colliding with Xemnas as he falls from the building as Sora is moving up, three Reaction Commands will appear over time, the first of which, "Clash", will cause Sora to pass Xemnas harmlessly. The second one, "Breakthrough", will cause Sora to attack Xemnas with a single attack, while the last one, which appears at the last second, will cause Sora to attack Xemnas several times and slam him into the skyscraper. Xemnas fights by teleporting around Sora, using Guard to push you back and make him temporarily invincible and swings his Ethereal Blades in perfect unison to constantly attack Sora. After the test Xemnas calls upon the power of the hearts to help him get stronger and he leaves. Afterward, Kingdom Hearts opens the door to Xemnas, letting you decide whether to face Xemnas right away or do other things in the game first.

Part 2 The Challanges
After Sora opens the door and enters he has to go through a series of challenges before getting to Xemnas. After the trials are over, Sora and party find Xemnas at the top of a robotic dragon sitting on a throne in full body armor. He uses a sword that attacks whoever touches it at least five times then sends them flying. He also uses the Guard ability to keep the party from attacking. After he is defeated, Sora and party find themselves back at the tower that they were at originally, and think they have won. A portal is created to help everyone get back to safety when Xemnas keeps Sora and Riku from getting through.

Part 3 The Dragon
When Sora and Riku find themselves trapped on a little Nobody ship, Xemnas sends his dragon and Nobodies to attack them. After bringing the dragon down, Xemnas takes them to another place in space. While the fight is the same as the previous one he launches Sora to the farthest place in the stage and sends lasers after him. Also, while Sora is fighting Xemnas, Xemnas has the ability to use all of the other Organization member's powers at the same time. Once he is defeated, Xemnas once again teleports them to another dimension. In here, he is more powerful and has more health.

Part 4 The Expert
Xemnas takes his gloves off in this last fight against Sora and Riku. He has the ability to teleport, to melt into the ground, and to fly. He constantly attacks Sora with lasers and lighting and sets off a huge series of reaction commands that Sora needs to complete to receive little to no damage. Throughout the fight, Xemnas will make a copy of himself to confuse Sora and will have the second act as a decoy. Late in the fight, Xemnas will capture Sora in an unescapable ray and Riku has to free Sora while fighting off the second Xemnas. On his last health bar, Xemnas will unleash his ultimate attack. The battlefield will turn dark and Sora and Riku become surrounded by lasers on all sides. Sora and Riku have to deflect the lasers for a few seconds and one mistake in blocking the lasers will result in certain death.

The End?
After Sora and Riku successfully defend against all the lasers, Xemnas starts to attack Riku, who is saved by Sora. Then, Sora and Riku together attack Xemnas with the unlocking beam of the Keyblade that goes through him. After the strike, Xemnas is paralyzed leaving Riku and Sora with an easy finshing move. Xemnas curses the Keyblade and passes with his hand stretched out toward Sora and Riku and breaks into nothing.

The Thirteen Seekers of Darkness
Due to Young Xehanort bringing Xemnas back from the past, he is among the versions of Xehanort summoned and made members of the True Organization XIII.