Uchiha Sasuke

When he was a child, he used to be a very kind boy, loving towards his parents and brother, and respectful to his clansmen and teachers. He was even very proud to being Itachi's brother and Fugaku's son, the ones who protect Konoha, and he always wanted to become like them. After Itachi massacred the clan, Sasuke's ideals and personality changed, becoming a cold, lonely sociopath, devoting his entire life to kill Itachi, who tossed him into the darkness. As Madara puts it, Sasuke has inherited the Uchiha clan's hatred, which makes him a true avenger.

When first introduced during his assignment to Team 7, Sasuke displayed a great indifference to his teammates. Feeling that his abilities were far superior to their own, he was unwilling to cooperate with Naruto Uzumaki or Sakura Haruno, as he felt that doing so would do nothing to help him kill Itachi. These perceptions were quickly proven wrong, however, for, despite their failings, Sakura was an excellent source of information, whilst competition with Naruto acted as an effective way to get stronger.

While he retained a confidence in himself throughout the series, Sasuke increasingly relied on his friends over the course of Part I. As he started to get close to others, he also began to risk his own life to save them, even though his death would have left him unable to fulfill his goal of vengeance upon Itachi. Although Sasuke became content with a life of happiness in Konoha, he never allowed his ambition to gain power to leave his thoughts.

During the Chūnin Exams, Orochimaru noticed how Sasuke's desire for revenge seemed to have lessened, and branded him with the Cursed Seal of Heaven to give him a taste of the power he could have if he kept to his previous path of vengeance. Even when Kakashi Hatake sealed the Cursed Seal, Sasuke began to draw more and more power from it with the hopes of getting stronger.

According to Kakashi, Sasuke has both superiority and inferiority complexes, as he has been unwilling to acknowledge when he is wrong or out of his league. While initially complacent with his development, Naruto quickly started to grow stronger at a faster rate. This, coupled with his quick defeat by Itachi during a brief return to Konoha, led Sasuke to believe that his growth was slowing. In an attempt to reassess his strength, he began to treat Naruto as an enemy so as to test his abilities against him, going as far as to kill with the Chidori, which Kakashi taught him to use to protect his friends.

Dissatisfied with his progress in Konoha, and believing that Orochimaru held the key to getting strong enough to kill Itachi, Sasuke defected from Konoha at the end of Part I, all the while ignoring the lecture that Kakashi gave him in an attempt to dissuade him from revenge. Naruto attempted to stop him, but Sasuke, believing the death of Naruto, his closest friend, would give him the power he desired (as he had been told by Itachi), tried to kill him instead. However, Sasuke was ultimately unable to follow through with this idea, as he felt that this was what Itachi would have wanted him to do, and instead continued on to Orochimaru.

In Part II, Sasuke showed that he had stayed true to his original personality; being extremely prideful and loyal to the Uchiha clan, as he always wore his clan's symbol and refused to wear the forehead protectors of both Konoha and Otogakure. In the two and a half years he spent with Orochimaru, Sasuke's goal to kill Itachi took precedence above all else; he even claimed that he was willing to give his body to Orochimaru if it meant killing Itachi, but Sasuke later turned on Orochimaru and revealed that he cannot forgive Orochimaru for attempting to steal his body, believing it is an insult to the Uchiha clan's pride.

Despite his coldness, Sasuke seemed to be unable to bring himself to needlessly harm those that had nothing to do with his quest for vengeance against Itachi and he made it a point to prevent their deaths when possible.[1] And while he told to Naruto and Sakura at their first reunion after 3 years, that he forgot them already, at the battle against Killer Bee and the Hachibi, it was shown that he still thinks about them. However, this attitude changed after Itachi's death. When Sasuke learned how his brother had been used by Konoha's elders to eliminate their clan, Sasuke abandoned all of his hatred for Itachi, and resolved to destroy all of Konoha for their actions against the Uchiha and how they used out Itachi's feelings for their own safety.

Overtime, Sasuke has grown crueler and more ruthless as his desire for vengeance drives him to point that he becomes willing to kill anyone who stands in his way as well as leaving his comrades to their fates. In addition, he also has no qualms in killing his former comrades. Sasuke's dark desire to kill Danzō has led even Sakura to finally lose hope in him and to aim to kill him (though she, like the majority of Konoha, has yet no knowledge of the massacre's true meaning and Sasuke's desire to kill Danzō specifically). His anger and hatred against Danzō is demonstrated in his willingness to crush Danzō into bloody pieces using Susanoo when Danzō insulted Itachi by calling him a traitor. Sasuke forbade Danzō from speaking Itachi's name, and shows anger when the elder defies that.

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 for revenge and power. Such girls include Sakura Haruno, Ino Yamanaka, Temari, Karin, and Mei Terumī; 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, the last time he was nice towards Sakura.