Kimimaro was the fifth member of the Sound Four, thus temporarily changing their group name to the Sound Five. The original four were forced to accept him against their will, as Kimimaro's combat abilities exceeded all of their skills combined. He was the sole survivor of the Kaguya clan, who could manipulate their bodies' skeletal frame. The Kaguya clan was wiped out when they attacked Kirigakure, seemingly for no reason other than the desire to kill. Having underestimated their opponent's defenses, they were slaughtered to the last man, with only Kimimaro surviving.
NOTE: Though some fans believe that his full name was Kimimaro Kaguya, the second databook only said his name as Kimimaro.
Kimimaro was referred to by Orochimaru as the most powerful member of the clan, having "abilities that even that war-loving clan feared". Because of this, he was locked away in a cage for most of his life, only released occasionally when needed to fight other clans.
Like many of Orochimaru's closest followers, Kimimaro was branded with a cursed seal, which gives him greater power at the expense of his free will. When in his level 2 form, his appearance is similar to that of a dinosaur, with dark gray skin, six large bone spines on the back of his chest, and a long bone spiked tail. He also possesses a great deal of control over his cursed seal, as he is able to control its spread throughout his body without fully activating it. Kimimaro was apparently friends with Jugo at one point, and his control over his cursed seal impressed the latter. Karin claims that Kimimaro was the only one who could stop Jugo without getting hurt.
(Source: Naruto Wikia)
