Orochimaru

Orochimaru's various human experiments take place so as to serve two purposes, most prominent of which is his desire to learn every jutsu in the Naruto world. Jiraiya speculates that this is due to the fact that his parents died when he was at a very young age, and flashbacks shown during his battle with the Third Hokage speak to this effect. Perhaps because he wanted to see his parents or as a means of avenging their deaths, he experiments on others to see what kind of modifications the human body can endure and to otherwise harness a subject's unique abilities for himself. Once accomplishing this goal, Orochimaru hopes to be worthy of the title of "ultimate being". Because a human's lifespan does not allow enough time to learn every jutsu, Orochimaru also experiments on others so as to achieve immortality. By living throughout the ages, Orochimaru need never worry about death and thus all the knowledge he gains will never be lost.

Above all else, Orochimaru cares only for himself. He grows bored when there is no conflict or violence in the world, and immediately strikes fear into others when they first meet him.Though he has a number of followers who would do anything for him, Orochimaru treats most of them as mere pawns, save for his right-hand-man, Kabuto Yakushi. He does not hesitate to send them to their deaths for his own personal benefit, and only finds remorse in their loss if they are unable to properly complete a task. To win over these followers to their disposable status, Orochimaru approaches them with promises of making their dreams, such as obtaining power, revenge, or a purpose to their lives, come true. He applies a cursed seal to many of his stronger subordinates in order to corrode their body and mind, making them more susceptible to his influence and control.