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. 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 will reduce everything to nothingness. The Rinnegan allows the user to use all of the six paths' techniques, as well as the seventh path — that is "beyond life and death".

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. Madara Uchiha would later awaken the dōjutsu as well after acquiring Senju DNA. This however 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. Tobi, while under the guise of being Madara noted 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 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.

Stated by Madara, the only ones who can unlock the rinnegan must hold the dna of a senju and the dna of the uchiha, Madara got it when figthing the first hokage and thus he unlocked it. Madara was able to transplant the rinnegan into nagato without him knowing, he did so because nagato was the only other person who could control the gedou mizou

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 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.

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.