Rinnegan

The Rinnegan is reputed as the most exalted eyes amongst the. It is characterised by its ripple-like pattern which spreads over the eyeballs, with light purple irides and sclerae.

Background
It was admired as being able to bring forth all 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 will reduce everything to nothingness. The Rinnegan allows the user to use the Six Paths Technique.

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. The Rinnegan can only be awaken by one who has and fully mastered the traits of the Uchiha and Senju DNA. This was proven when Madara Uchiha would later awaken the dōjutsu by infusing Hashirama Senju's DNA into him; however it did not manifest until he was near the end of his life. At some point after this, he would implant his eyes into Nagato — a young Senju descendant. Obito Uchiha, being the partner and given the guise of Madara, he believes that since it was given to Nagato by Madara, he is entitled to taking the Rinnegan from Nagato's body after his death. He implants one of the Rinnegan in his left socket, replacing the Sharingan he sacrificed.

When Madara was reincarnated by Kabuto Yakushi, to fight the Allied Shinobi Forces, Madara once again gained access to the dōjutsu; Eternal Mangekyō Sharingan transformed into the Rinnegan. Based on data collected over the years, Kabuto Yakushi and Orochimaru theorised that because the Sharingan originated from the Rinnegan, it was possible for the dōjutsu to devolve into the Rinnegan as part of a "natural evolution". This is supported by the fact he maintains his Susanoo while having his Rinnegan activated. Upon reincarnation, Nagato also retained the Rinnegan.

Abilities
Like the Mangekyō Sharingan and Sharingan, the Rinnegan has shown the ability to control tailed beasts through the use of the Outer Path's ability with its chakra chains and receivers. The holder of these eyes have the potential to completely master all five basic nature transformations that form the basis of ninjutsu.

The Six Paths of Pain were all reanimated corpses that Nagato could control with the Rinnegan. By doing so, Nagato could see each individual body's field of vision, coordinating the bodies with extremely precise planning. The animals summoned through the Animal Path also possessed the Rinnegan, so Nagato controlled and also shared a field of vision with them and the King of Hell with the use of the Outer Path technique. 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. One who has naturally manifested the Rinnegan, like Madara Uchiha, is able to switch their eyes' form between it and any of it and any previous Sharingan forms at will. Those with a transplanted Rinnegan, however, show no such ability.

Trivia

 * In the anime, the Rinnegan was depicted as being multicoloured in its first few appearances. Once coloured manga illustrations of the Rinnegan were released, this was corrected.
 * In Naruto: Shippūden episode 203, a silhouette of the Sage of the Six Paths is shown. Here, the Sage's Rinnegan is shown to be red instead of the usual colour.
 * is the Japanese term for Samsara, the cycle of reincarnation or rebirth in several Indian religions. This is reflected in the names of all Six Paths of Pain, which share the names with Samsaric realms of reincarnation.