When he was a child,
Sasuke used to be a very kind boy, loving towards his parents and brother, and being respectful to his clansmen and teachers. He was even very proud of being Itachi's brother and Fugaku's son, famous for being devoted protectors of Konoha, and he always desired to emulate them. After Itachi massacred the clan, Sasuke's innocence was corrupted, his ideals and personality changed severely, becoming cold, lonely, cruel, cynical, somewhat arrogant, and with the next eight years of his life devoted to killing Itachi.
When first introduced to Team Kakashi, Sasuke displayed great indifference to his team-mates. Feeling superior to all of them, including his teacher, Sasuke was unwilling to cooperate with Naruto Uzumaki or Sakura Haruno, as he felt they would provide him no aid in killing Itachi. However overtime, as he spent more time with his team, Sasuke began to lose some of his anger, caring more about his team than his revenge. To help push him back into his desire for power, Orochimaru branded Sasuke with the Cursed Seal of Heaven during the Chūnin Exams to give him a taste of power. Although Kakashi Hatake sealed the Cursed Seal, as well as teaching him the Chidori in the hopes of deviating him from the path of revenge and instead protect his current friends with it, Sasuke began to draw more power from the seal in the hopes of getting stronger, as well as warp the Chidori into a blade to sever friendship.
According to Kakashi, Sasuke has both a superiority and inferiority complex, as he is unwilling to acknowledge when someone is stronger than him, but obsesses when he believes someone is stronger than him. For example, he was complacent with his rivalry with Naruto when he believed he was stronger, but noticing Naruto's fast growth, coupled with his defeat of Sunagakure's jinchūriki Gaara where Sasuke was beaten, and his quick defeat by Itachi on his return to Konoha led Sasuke to believe that his progression at Konoha was far too slow, which lead to his defection to Otogakure. Upon defected from the village, Sasuke left with the Sound Four and traveled to the Land of Sound, only to lose the entire Sound Four to the Sasuke Retrieval Team and face Naruto alone at the Valley of the End, where Naruto attempted to save him from his path of revenge. Sasuke in turn planned to kill Naruto, his closest friend, to awaken his Mangekyō Sharingan but upon his victory chose against it, instead vowing to beat Itachi his own way.
In Part II, Sasuke's personality reverted to about the same as when he first met Team 7, although his revenge against Itachi took precedence above all else, including his own life. He also claimed to have cut all ties to his life in Konoha, believing that they were the cause of his weakness, going as far as attempting to kill Naruto, whom he spared in their previous battle, to prove how detached he was. Despite this, Sasuke seemed unwilling to needlessly kill in his quest for revenge,[4] and later when battling Killer Bee and the Eight-Tailed Giant Ox, Sasuke remembered Team Kakashi after witnessing his own team Taka each sacrificing themselves to help him.
Sasuke's personality change.
After his battle with Itachi, followed by his death and the revelation that Itachi was ordered by the Konoha Elders to kill the Uchiha clan and that Itachi truly loved him, Sasuke vowed to destroy Konoha to the last child for sacrificing Itachi and the Uchiha clan for their own happiness. Although at first still holding onto the notion of friendship and sparing the innocent, as time passes on with this new path of revenge, Sasuke had grown much crueler and more ruthless, killing anyone who stood in his way, sacrificing his own team to accomplish his goals and attempting to kill his former team-mates and teacher, experiencing neither shame, guilt, nor remorse for his actions. He had also shown great rage when someone speaks of Itachi in a negative way, crushing Danzō with his Susanoo for speaking ill of his brother. After killing Danzō, Sasuke felt an exhilaration that he never felt before, and even sees killing members of Konoha as a high, which leads him to vow to kill everyone in the village to finally separate any connection of the Uchiha clan from the village and in doing so purifying the name. At this stage it is clear that Sasuke has hit rock bottom with his hatred, leading Sakura and Kakashi to lose all hope in him, and even Karin, despite being obsessed with him, has given up being with him. The only person still having some faith in him is Naruto. Sasuke, in turn, abandoned his refusal to transplant Itachi's eyes into himself, in the hopes of destroying all that Naruto stands for with his full power, due to him hating Naruto more than anything for refusing to give up on him.
When Sasuke felt he had grown stronger than Orochimaru, he saw sacrificing his body to someone weaker than him was insulting to the Uchiha, despite claiming earlier that he did not care if it served to his revenge. He proceeded to battle and absorb Orochimaru's conscience when the latter attempted to steal his body. This is due to Sasuke's immense loyalty to his clan, and that he remained wearing its symbol on his back proudly, when he refused to wear any other symbols such as a forehead protector. He also saw that anyone outside of the clan wielding the Sharingan as an insult, as the eye is a symbol of the Uchiha's powers; while Itachi and Madara complimented Kakashi's mastery over the Sharingan gifted by Obito, Sasuke expressed resentment at an outsider even possessing it, and that Kakashi should feel grateful to the Uchiha for the power. Sasuke showed further disgust when Danzō had ten Sharingan in his arm, and an eleventh one in his right eye.
Also, for his entire life, despite being popular towards females due to being handsome and cool, Sasuke showed absolutely no interest in any of these women, nor their advances, due to his only desire being for revenge and power. Such girls include Sakura Haruno, Ino Yamanaka, Karin, and even the Fifth Mizukage. Even when Sakura's childish crush turned to sincere affection, Sasuke still did not return the feelings, though before he left the village, he gave Sakura a genuine thank you. His disinterest in these women can turn to murderous violence, expressed during his fight with Danzō, where he stabbed Karin to kill Danzō, and during his fight with Team Kakashi, where he attempted to kill Sakura twice.
Appearance
Sasuke in his second stage Chūnin Exams outfit.
Sasuke has black hair with a blue tint, which lengthens as the story progresses, and onyx eyes. He has lighter skin than his older brother, Itachi, had. Like many other members of his clan, his hair hangs over both sides of his face to roughly frame his cheeks. A recurring theme in Sasuke's appearance is that he is considered quite handsome by almost all girls near his age. At the beginning of Part I, Sasuke's clothing consisted of a blue, short-sleeved shirt with a raised collar and the Uchiha crest on the back, and white shorts. In the last stage of the Chūnin Exams, he wore a black, one-pieced version of this outfit with many small arm-belts adorning his left arm, but eventually went back to his original clothes, due to the creators having a difficult time drawing this version on a regular basis. As the story progressed the Uchiha symbol became smaller and smaller.
Initially, Sasuke wore a short blue-colored headband with the Konoha symbol on the metallic plate. After suffering a second defeat from Itachi, Sasuke stopped wearing it for a time. He put it back on during the latter half of the battle with Naruto at the Valley of the End, only to let it drop off at the end. After that, Sasuke hasn't worn a headband again.
In Part II, Sasuke has grown noticeably taller over the two and a half years and more muscular. He was first shown wearing a white long-sleeved shirt which was open at the torso, with a smaller version of the Uchiha crest on his collar. He wore black pants with a blue cloth hanging from halfway up his stomach to his knees. He also wore a purple rope around his waist, tied in a bow. After battling Deidara, he switched to a sleeveless dark gray shirt. His arm guards were also removed, and he started wearing bandages on his wrists, under which are seals where he stores shurikens. He also wore a cloak with this.
After he encountered and battled Itachi, he reverted to a gray shirt with a raised collar which was unzipped halfway down his chest, similar to the one he wore at the start of Part II, but with shorter sleeves. He also wears blue wrist warmers. He briefly wore an Akatsuki cloak along with this. Another noticeable trait is that, along with this new outfit, Sasuke began letting his hair hang over his eyes.
Overall, Sasuke bears a striking resemblance with Izuna Uchiha.