Naruto and Sasuke are forced to cooperate against their will when they were both put in Team 7 together with Haruno Sakura, who has a huge crush on Sasuke. Naruto initially has a one-sided rivalry with Sasuke, because Naruto aspires to be what Sasuke appears to be, but Naruto was unable to obtain during his time at the Ninja Academy; Unlike Naruto, Sasuke has received recognition for his talent, popularity and admiration while Naruto received ridicule for his apparent lack of ninja talent, and was shunned or scorned otherwise. Sasuke initially looks upon Naruto and his admirer, Sakura, with an equal smug distaste, viewing them as annoyances who would only get in the way. His loner attitude is one of the negative factors responsible for Team 7's initial state of borderline non-existent teamwork, which Kakashi notes and berates him for; however, their relationship slowly shifts from an incompatible mix of frustration and dislike into a mutually positive rivalry. While Sasuke appears to always be one step ahead to Naruto, Sasuke sees Naruto as constantly gaining ground each moment, which results in a state where they push and motivate each other to improve.
Uchiha Sasuke.Sasuke makes it a point to taunt Naruto on occasion, goading and egging on Naruto with his air of superiority. However, a bond between the two and Sakura forms and Sasuke gradually learns the value of teamwork. As he does, he eventually begins to learn to trust and pushes his thoughts of revenge into the recesses of his mind.
This does not please Orochimaru, who is interested in Sasuke as his next potential body, since the Sharingan's technique copying ability would help greatly in Orochimaru's ambition to master all jutsu in the Naruto world. Orochimaru decides that it is imperative to somehow counter Naruto's influence on Sasuke and "dye him to his own color". To advance this cause he puts his cursed seal on Sasuke during the second stage of the Chūnin exam, which coincidentally has the same design as a fully-developed Sharingan. Sasuke turns out to be strong enough to survive the nine out of ten chance of death from the seal and regains consciousness, but its influence is far from over. Just from molding his Chakra, the cursed seal activates and drains Chakra, while causing intense pain, corroding his body and his free will. At this point the small mark on the neck spreads over Sasuke's whole body, covering him in a black flame-shaped pattern.