The Rinnegan (輪廻眼; Literally meaning "Samsara Eye") is characterised by a ripple-like pattern over the eyeballs, with a light purple iris and sclera. It is said to be the most powerful of Three Great Dōjutsu (三大瞳術, San Daidōjutsu; Literally meaning "Three Great Eye Techniques"). It was admired as being able to bring forth all ninjutsu. The holder of these eyes can completely master all five basic nature transformations that form the basis of ninjutsu. It was said that in times when the world is in disorder, a person is sent down from the heavens to become either a "God of Creation" who will calm the world, or a "Destroyer" who reduce everything to nothing. It also allows the user to use all of the six paths techniques, as well as the seventh path - that is "beyond life and death".
The Six Paths of Pain were all reanimated corpses that Nagato gave the Rinnegan to through some unknown means. By doing so, Nagato could see each individual body's field of vision, coordinating the bodies with extremely precise planning. The animals summoned by the Animal Path also possessed the Rinnegan, so Nagato controlled and also shared a field of vision with them and the King of Hell. On its own, the Rinnegan allows the user to see chakra, including otherwise hidden barriers. It can also decipher more of the Sage of the Six Paths' tablet than the Sharingan and the Mangekyō Sharingan are able to.
Obtaining the Rinnegan
The first person to possess the Rinnegan was the Sage of the Six Paths. Because of the Sage's mythical status, many people believed the Rinnegan was only a legend or a mutation. It later showed up in Nagato during his childhood. Tobi claims that he gave Nagato the Rinnegan. For this reason, he believes he is entitled to taking the Rinnegan from Nagato's body after his death. He implants one of Nagato's Rinnegan in his left socket, replacing the Sharingan he lost to blindness.
Through unknown means, both Madara Uchiha and Ryun Uchiha managed to awaken the Rinnegan from their Eternal Mangekyō Sharingan. In his battle as a reanimated corpse against the Alliance, Madara's Eternal Mangekyō Sharingan transformed into the Rinnegan. Based on data collected over the years, Kabuto Yakushi and Orochimaru hypothesized that this is a natural evolution, and that the Rinnegan is the final stage of the Sharingan.