Orochimaru is a fictional character of the manga Naruto. He is one of the greatest villain of the story, as well as a very powerful and dangerous ninja. He was formerly a ninja of Konoha, but defected 10 years before the beginning of the story, because his research about a technique which could allows him to live for the eternity were discovered. He then created his own village, and vowed to destroy his former home. When he was a ninja of Konoha, he was the most brilliant pupil of the 3rd Hokage, the boss of the village, and was considerated to be one of the most powerful ninja of the entire village, the 3rd even wanted him to succeed him as the chief Konoha.
In the first part of the series, Orochimaru tried to destroy his former home, invading it with an army of ninja, and killed his former master, but failed to destroy completely the village. He later take Sasuke Uchiha as his apprentice, but was betrayed by him after training him during two years. Sasuke attacked Orochimaru when he was close to death, but Sasuke couldn't kill him and absorbed him in his body instead.
During the fight between Sasuke and his brother Itachi, Orochimaru was able to come out of Sasuke's body, but was quickly defeated by Itachi, who imprisoned him in a eternal illusion.