Orochimaru (大蛇丸, Orochimaru) served as the central antagonist for the majority of the series during Part I but later became a secondary antagonist during Part II. Recognised as one of the most powerful ninjaKonohagakure ever produced and one of the "Three Legendary Shinobi" (伝説の三忍, Densetsu no Sannin), he operated as an ANBU shinobi within the Root faction prior to his defection from the village in pursuit of his own self-serving ambitions. Initially sealed away during the battle between Sasuke and Itachi Uchiha by the latter, he was later reconstituted by the former using his own genetic material that was within his successor Kabuto Yakushiand a copy of consciousness he stored within Anko Mitarashi's Cursed Seal of Heaven.

 

  Orochimaru was an orphan who became a pupil ofHiruzen Sarutobi alongsideJiraiya and Tsunade. Compared to the more laid back Jiraiya, Orochimaru stood out as a genius — his talents, knowledge, and determination were considered by Hiruzen to be that of a prodigy seen once in a generation. According to Tsunade, Orochimaru had a twisted personality even as a child. His sadistic attitude was presumably due to the death of his parents. At some point after losing them, Orochimaru found a white snake near his parents' grave, with Hiruzen explaining that it represents fortune and rebirth inspiring Orochimaru to study kinjutsu and obtain knowledge of all techniques. Jiraiya theorised that Orochimaru went down this path in an attempt to forget his painful memories. In the anime, Orochimaru later witnessed Itachi performing a training run normal meant for older and more experienced users due to the danger of it. After the young Uchiha flawlessly completed it, Orochimaru instantly became amazed and excited at Itachi's advanced growth rate. 

 

  During the Second Shinobi World War, Orochimaru joined Jiraiya and Tsunade in fighting Hanzō, who gave them the title of Konoha's "Three Legendary Shinobi" (伝説の三忍,Densetsu no Sannin) as a reward for surviving their battle with him, while the rest of their group were easily slaughtered in the process. On their way back to Konoha, they encountered three Amegakure orphans, with Orochimaru proposing a mercy killing before Jiraiya chose to train them instead. In the anime, Orochimaru orchestrated the last known rampage of the Eight-Tails inKumogakure by infiltrating the village while disguised as a Kumo-nin and posing as Fukai's doctor in order to trick him into taking special genjutsu inducing pills to bring forth the Eight-Tails to attack Kumogakure. After the rampage, Orochimaru obtained that severed horn of the Eight-Tails's horn and harvested Fukai's DNA from it.

 

  Some time after Team Hiruzen was disbanded, Orochimaru became an ANBU member and joined Root to work directly under Danzō Shimura, while also becoming a mentor to Anko Mitarashi. It was during that time that Orochimaru met Kabuto Yakushi while accompanying Danzō in forcing the boy's guardian Nonō into a mission. While Orochimaru's ambitions did include becoming the Fourth Hokage, he intended to use the title for his own agenda. Though Hiruzen knew the potential evil his former pupil had in him, he hoped to stir Orochimaru from the path before slowly realising that he was beyond anyone's help.  

 

  Orochimaru was later sent on a mission by Danzō toIwagakure to ensure that both Kabuto and Nonō, the former having joined Root as a spy, killed each other as they had become major risks. Orochimaru, instead, spirited Kabuto to his hideout, what would become part of his personal hidden village, Otogakure, and revealed Root's intent for Kabuto's life and the role he was to play in it. Though Orochimaru revealed that he was also sent to kill the one who survived this ordeal, he told Kabuto that he saw a bit of himself in the boy and decided killing him would be a waste of great talent. Therefore, Orochimaru offered Kabuto a position as his right hand and spy with the promise of an identity. With Kabuto's assistance, he performed various experiments on his prisoners, some being fellow Konoha shinobi he kidnapped. He uses them as human guinea pigs to develop techniques that would grant him immortality, the end result being Living Corpse Reincarnation. Some time later, Orochimaru was at the outskirts of Kirigakure as he found Kimimaro, the sole survivor of the Kaguya Clan. Soon after, thanks in part to Kimimaro, Orochimaru's research on the source of Jūgo's powers led him to find the Ryūchi Cave and master senjutsu. Unable to enter Sage Mode because of the fragility of his host body, Orochimaru instead developed an alternate method of harnessing his senjutsu chakra throughcursed seals, which he tested on Anko and several others before eventually using the finalised versions on Kimimaro and the Sound Four. 

 

  When Hiruzen finally retired and named Minato Namikaze his successor, Orochimaru saw no more reason to remain in Konoha and began to be less discreet with his actions. This led to his experimentation on the cultivation of Hashirama Senju's DNA with sixty children he kidnapped to recreate the First's Wood Release techniques, having already done so with Danzō, while also endowing the elder with multiple Sharingan. However, as his test subjects began to die off, Orochimaru was caught red-handed by Hiruzen, who knew it was his duty to kill him yet lacked the will to do so. Leaving Konoha and his emotionally broken mentor, with Jiraiya's pleas for him to reconsider falling on deaf ears, Orochimaru was unaware that one child had survived his experiment. 

 

  Orochimaru soon joined the elite criminal organisation Akatsuki, his role in which was unclear, although he was partnered with Sasori, whom he did much good for the Akatsuki with. However, when Itachi Uchihajoined Akatsuki after conducting the Uchiha clan massacre, Orochimaru saw his opportunity to steal his body to gain possession of the Sharingan. Itachi used his Sharingan to stop him from doing so, while also cutting Orochimaru's left hand off to prevent him from breaking thegenjutsu he was under, which lead to him leaving Akatsuki to acquire a new body. For Orochimaru's defection, Sasori developed a grudge against him and used Kabuto, whom Orochimaru had sent to serve as his spy within Akatsuki, to counter spy as his sleeper agent. However, Orochimaru discovered and undid the technique Sasori had used on him.Orochimaru had also been on a life-long search for the Totsuka Sword, an ethereal sword, but was unaware that it was in the possession of Itachi's Susanoo.