Sasuke Uchiha is one of the top scorers of the ninja apprenticeship school and the top "Genin" (rookie/first-level ninja) of the Village Hidden in the Leaves. He is the sole remaining member of the Uchiha clan, a once powerful ninja clan of the village. He is very dark and serious, and is focused on nothing else but training to become a stronger ninja.

All of this is for one ultimate goal: revenge. His life's ambition is to grow powerful enough to kill "a certain man" (his older brother Itachi). As part of the Uchiha clan, Sasuke has higher "chakra" (spirit energy/chi). He also has a technique to blow fireballs from his mouth.

Also, as one of the Uchiha clan, he inherits the clan's Kekkei Genkai (or bloodline trait)--the Sharingan. He begins to unlock it in the fight with Haku (who himself was using a Kekkei Genkai) and it gradually gains strength as he learns to use it to track movements and observe ninjitsu techniques. It helps having a knucklehead like Naruto as a teammate. He doesn't like Naruto at first, but as they and Sakura learn to work as a team, he shows a surprising willingness to protect Naruto. It's the beginning of a pretty complex teammate/rival relationship, as each watches for the other but at the same time wants to become better than the other. Sasuke's Sharingan eyes attracted the attention of an extremely dangerous S-ranked criminal, Orochimaru. Orochimaru gave Sasuke the cursed seal, because he wanted Sasuke's body after he truly became strong. When Sasuke fought Naruto, they each use a powerful jutsu. Naruto use Rasengen and Sasuke uses Chidori. Chidori, also known as Raikiri (Lightning blade), is a jutsu taught to him by Kakashi. After watching Naruto become strong so quickly, Sasuke felt inferior and as if he hadn't gotten better at all. Orochimaru used this chance to send some of his shinobi (Sound Four) to bring Sasuke to him. Sasuke went willingly, because Orochimaru promised him power. Thus, Sasuke became a traitor of Konohagakure. For Sasuke to have the same eyes as Itachi, he has to kill his best friend. Although he initially hates Naruto with a passion, he eventually becomes his best friend. At the end of a battle with Naruto, Sasuke is the winner. Sasuke hesitates, striking Naruto with the back of his hand instead of the Chidori, thus sparring Naruto's life, as he realizes that killing Naruto to obtain the same eyes as Itachi, would be exactly what Itachi wanted. Sasuke leaves Naruto on the ground unconscious, but alive.