Orochimaru

Orochimaru is one of Konohagakure's legendary Sannin. With a life-ambition to learn all of the world's secrets, Orochimaru seeks immortality so that he might live all of the lives necessary to accomplish his task. After being caught red-handed performing unethical experiments on his fellow citizens for the sake of this immortality, Orochimaru defected from Konoha rather than be persecuted for his ambitions, and for many years sought the village's destruction in order to take revenge and demonstrate what he had learned. After several apparent deaths in the pursuit of his goals, Orochimaru realises his approach is flawed through Kabuto Yakushi, his former associate, and begins monitoring the choices and actions of his former apprentice, Sasuke Uchiha.  Orochimaru was an orphan who became a pupil of Hiruzen Sarutobi alongside Jiraiya 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 only 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's explanation of it representing 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. 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" 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 in Kumogakure by infiltrating the village while disguised as a Kumo-nin and posing as Blue B's doctor in order to trick him into taking special genjutsu inducing pills, allowing him to extract the tailed beast. After its rampage, Orochimaru obtained the severed horn of the Eight-Tails and harvested Blue B'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. When Hiruzen finally 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 Hashirama Senju's DNA with sixty children he kidnapped to recreate the First's Wood Release, having help from Danzō. Believing it to be a failure, Orochimaru was unaware that one child had survived his Wood Release experiment. He later refined the process enough to inject Hashirama's cells into the Sharingan-infused right arm of Shin Uchiha, which he transplanted to Danzō. Orochimaru performed various experiments on his prisoners, some being fellow Konoha shinobi he kidnapped. He used 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 through cursed seals, which he tested on Anko and several others before eventually using the finalised versions on Kimimaro and the Sound Four. In the anime, Orochimaru found the Iburi clan living underground near Konoha. Taking an interest in their ability to become smoke, Orochimaru took advantage of the clan's fear of their imperfect and potentially fatal transformation by partially stabilising it with his cursed seals. Telling them that he needed more research to perfect the process, the clan willingly gave Orochimaru test subjects. In the anime, Orochimaru witnessed Itachi Uchiha performing a training run normally 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. In the anime, he also allied himself with Amachi out of interest for creating a shinobi capable of underwater combat, kidnapping Land of the Sea villagers for their experiments, while introducing Anko to the project. Sometime after, Orochimaru lost interest in the project, and ordered Amachi to cancel it, while also seeing Anko as a lost cause for her refusal to use the cursed seal, and wiped her memories as she left him. Orochimaru was later sent on a mission by Danzō to Iwagakure to ensure that both Kabuto and Nonō, the former having joined Root as a spy, killed each other as they had become major liabilities. Orochimaru instead spirited Kabuto to his hideout, which 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.