Gen'yuumaru (幻幽丸) was a prisoner one of Orochimaru. He is forced to fight his fellow prisoners with the understanding that the survivor will be set free. When he wins he discovers that his body will become Orochimaru's next vessel. Knowing there is nothing he can do to escape this fate, Gen'yuumaru asks that his clan members that are also imprisoned be set free. In Part II, after Gen'yuumaru's body begins to reject Orochimaru and he attempts to take Sasuke Uchiha's body, Gen'yuumaru is seen in Orochimaru's subconscious along with his other former host bodies' souls.

(Source: Narutopedia)