Dosu Kinuta was the leader of the Sound ninja team recruited by Orochimaru to test the power of Sasuke Uchiha, under the false guise of assassinating him. His introductory scene was when he, alongside his teammates Zaku Abumi and Kin Tsuchi, were pointed out by Kabuto as being from a village that had no background or importance in the Chuunin Exams. Hearing the statement, he took it as a direct insult to who he was and what he was doing. With Naruto shouting out that he would "never lose to these idiots", he ran forward and attacked Kabuto, proving that he was not someone to be messing with and that Sound ninja could be quite "vicious".
Of course, it was later stated that even Kabuto, being the elite Sound nin that he was, was caught off guard by Dosu's attacks, and was unaware that they were actually willing to attack someone. He complimented Orochimaru for picking such willing subordinates for the job.
For years Dosu had seen Orochimaru as a father figure and friend, and he was the most powerful Sound genin. Dosu was initially unaware that Orochimaru had no intention of Sasuke dying during the Chuunin Exams.
Dosu and his team ambushed Sakura and the unconscious Sasuke and Naruto in the second test of the Exams: the Forest of Death. However, they are unable to achieve their goal of killing Sasuke, due to the interference of Rock Lee (who Dosu incapacitated quickly), Team Asuma, and the Cursed Seal-empowered Sasuke. In the process, Kin falls unconscious and Zaku's arms are broken by Sasuke. Dosu retreats and picks up his fallen teammates before conceding to Sasuke's powers and vowing that he wouldn't run next time. It is then that Dosu catches a whiff of Orochimaru's plan, realizing that he and his team were only meant to test Sasuke's abilities.
In the third round of the Exams, the tournament round, Dosu was put up against Choji. His opponent used the Body Expansion jutsu and charged after him, but Dosu dodged and guided him into the building's wall, where he knocked him out with the Melody Arm. He then proceeds to the Chuunin Exam finals with one goal in mind: to ruin Orochimaru's plans and kill Sasuke himself.
However, his desire to fight Sasuke overpowers his better judgment. In the month between the Exam tournament's preliminaries and its finals, Dosu attempts a preemptive strike on Sasuke's next opponent, Gaara. Dosu cockily challenges Gaara and is swiftly defeated by the inhuman power of the Shukaku.
Dosu's face was never shown throughout the series because of his bandages. It is never stated whether or not the bandages meant anything to him, and why he wore them, much less why he covered one eye with them. He also wore a long fur scarf which gave him an awkward appearance due to its fuzzy outline. His posture was poor, and he was always hunched over in a primal stance, making him look even more awkward.
Kinuta's clan was never shown, and as far as we can discern, his eye color was black. He was covered up quite thoroughly as to make him seem more mysterious, maybe, or Masashi Kishimoto just wanted to try a new design. Dosu spoke softly, but when he did, he spoke with force behind his words. He never backed down from anything, other than Sasuke in his curse marked form, and that was only because he was worried about his teammates' safety. He was also clever and intelligent, as shown when he discovered one of Sakura's traps just from her throwing a kunai at a nearby squirrel.
Dosu stands out from Orochimaru's other minions in that he was one of the few that was able to see through Orochimaru's trickery. He was able to deduce Orochimaru's plans and realized that his team was expendable, which caused him to rebel.
Despite his harsh demeanor, Dosu was shown to have a protective attitude towards his teammates. He was always looking out for them, even though he had practically nothing in common with them. In the Forest of Death, he showed a fair amount of concern for his two teammates, and he was constantly warning them not to charge ahead recklessly (which they did anyway). He also checked in with his teammates and offered them advice before their respective rounds in the tournament. Later, when Zaku's arms were blown off by Shino, Dosu vowed that he would avenge his teammate and defeat Shino.
Powers and Abilities
Dosu used the mechanism on his arm (the Melody Arm) as an amplifier to fight with, using his chakra to manipulate the sound waves at will. With this technique he was able to make a completely unblockable attack. He could use this sound to confuse and distort an enemy's senses, making it hard for the victim to balance, or even to destroy things (he used sound to destroy a log in the Forest of Death).
He also had superb hearing; he could detect what someone was writing just by listening to the scratches their pencil was making. He demonstrated this ability in the first round of the Chuunin exams.
He was skilled enough to be considered an "elite rookie" by Sasuke, who compared his power to that of Rock Lee, Neji, and Gaara.