Sasuke is arguably the best character to come out of Naruto. The way that he was developed and allowed to grow despite being outside of Konoha and away from the rest of the protagonists makes him one of the more mysterious characters of the series.
The way that Sasuke Uchiha is presented in the series amplifies the interest surrounding him. He was introduced as being a talented prodigy in the ninja arts. In the days when the group was still in school, he was the star student displaying talents that exceed expectations. Despite the popularity that resulted from his clearly superior abilities, he was shown to be detached from the rest of the class and even from the members of Team 7. He was constantly seen brooding and thinking about his goal to kill his brother, a goal that grew from his experience in the past. Having returned home to his entire clan being slaughtered at the hands of his now criminal brother, Sasuke carried the will to end his brother’s life and avenge his clan.
The reason however that I personally find Sasuke interesting is because of the role that he plays in the series and how his character is built next to the titular character Naruto. The two are depicted as rivals throughout the series and while this is quite common in shounen, I felt that the rivalry between the two was unique because of their characterization and how Sasuke was built in direct relation to Naruto.
The two shared enough or were similar enough to allow for a legitimate and organic connection. Both Sasuke and Naruto were orphans who had lost their families early on in their lives. They grew up with the lack of experiencing the warmth and love of parents. In this sense, both characters had the same hole to fill. It was precisely this similarity that actually brought the two together forming a strong bond and connection between Naruto and Sasuke. They established a familial tie with one another regarding each other as brothers in a sense. Rather than being strictly rivals who were aiming for the top, the two formed a bond over their loneliness and managed to find a family in Team 7 and more importantly in one another. It was also this well developed bond that drove Naruto to chase after Sasuke when the latter had intended to leave Konoha for good. Rather than let him go, Naruto chased after Sasuke, one who he regarded as a brother, and tried to stop him from leaving and going so far as to engage him in combat to do so.
Naruto and Sasuke were also different enough that their rivalry made absolute sense. Sasuke was always depicted as being the prodigy and the extremely talented shinobi even among his peers. He was advanced in terms of ninjutsu and displayed natural prowess in all other aspects of combat. In contrast, Naruto was initially a character who was mediocre in everything but drive. He was shown as being incapable of most forms of ninjutsu and was also not as capable as his other classmates. His techniques were far from refined especially when seen next to the flawless performance of Sasuke. Sasuke was always depicted as being ahead of Naruto in terms of his breadth of knowledge and ability and this eventually made him a target for our protagonist. He was a symbol for an almost unattainable goal. This carried over to Naruto’s inability to take Sasuke back to Konoha after he had left despite having multiple opportunities.
What sets Sasuke apart however is how he was never truly a protagonist nor an antagonist. Rather, he was a character that was in the gray for almost the entire series. His role was to embody the goal of Naruto and to act as his foil. In fact, he was one of the major reasons that Naruto even improved. Instead of playing the clear villain, he was a character who represented what Naruto strived for albeit on the darker side of the spectrum. I personally felt that it was this aspect of Sasuke’s character that made him so popular and likable throughout the entirety of Naruto’s run.