Rinnegan

The 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 sclerae and irides.

Background
The Rinnegan was admired as being able to bring forth all ninjutsu. It is 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 down the world, or a "Destroyer", who will reduce everything to nothingness. The Rinnegan allows the user to perform the Six Paths Technique.

The first person to possess the Rinnegan was the Sage of the Six Paths. As a result of the Sage's mythical status, many people believed the Rinnegan was only a legend or a mutation. Because the Rinnegan was originally wielded by the Sage of the Six Paths, re-merging the chakra of his two sons, Indra and Asura, in one's body can lead to that person awakening this dōjutsu. This was proven when Madara Uchiha, Indra's reincarnation at the time, later awakened the dōjutsu by infusing the DNA of Hashirama Senju, Asura's reincarnation at the time, into his body; however, it did not manifest until many years later when he was near death. At some point after this, Madara would implant his eyes into Nagato — a young boy of Senju lineage. Under the guise of Madara and inheriting the former's work, Obito Uchiha claimed that he was entitled to take the Rinnegan from Nagato's body after his death. He then implanted the left Rinnegan into himself, 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; he was able to transform his Eternal Mangekyō Sharingan into the Rinnegan at will. Based on data collected over the years, Orochimaru and Kabuto theorised that because the Sharingan originated from the Rinnegan, it was possible for the dōjutsu to change into the Rinnegan as part of a "natural evolution". However, upon Madara's true revival as a living being, he no longer possessed his eyes, as they were but a reflection of his former self due to him dying without his actual eyes. A White Zetsu clone managed to retrieve the right Rinnegan from where Obito had hidden it and returned it to Madara's previously empty right socket.

After receiving half of Hagoromo's power, Sasuke's left eye transformed into what Madara referred to as the Rinnegan. The dōjutsu has the typical concentric circles but also has tomoe reminiscent of the third eye Kaguya Ōtsutsuki possessed, and the Ten-Tails' singular eye.

Abilities
One who gains the Rinnegan has access to a multitude of abilities. The holder of this dōjutsu has the potential to completely master all five basic nature transformations, and the capacity to use any technique. The Rinnegan allows the user to see chakra, including the chakra points within the body,  otherwise hidden barriers, and even invisible targets. However, the Rinnegan's field of vision can be blocked by such things as dust clouds, smoke bombs, and mist. The dōjutsu can also completely decipher the Sage of the Six Paths' tablet, unlike the Sharingan and Mangekyō Sharingan. A noteworthy power of the Rinnegan is the ability to summon and control the Demonic Statue of the Outer Path, though this cannot be done using a Rinnegan created through Summoning: Impure World Reincarnation. As seen from Sasuke, the Rinnegan can also teleport the user or other targets into another location, and augment one's nature transformation, such as turning a Lightning Release into a darker version.

One of the Rinnegan's trademark techniques is the Six Paths Technique, which grants the user multiple abilities known as Paths. The Deva Path can be used to attract and repel targets. The Asura Path can clad the user in mechanised armour and grant them various weapons. The Human Path can read minds, at the cost of ripping out the victim's soul. The Animal Path can summon several different creatures. The Preta Path can absorb any chakra-based ninjutsu. The Naraka Path can summon the King of Hell, which can be used for interrogation and restoration.

Finally, the user is granted the Outer Path, which gives them control over life and death. It also allows the user to manifest chakra chains, which can be used to bind and control tailed beasts in a similar fashion to the Sharingan and Wood Release. It can also manifest chakra receivers and wield them, even produced from another unharmed. Using these rods embedded in another target combined with the Outer Path grants a shared field of vision between the Rinnegan wielder, the creatures summoned through the Animal Path and reanimated corpses, which also have the user's Rinnegan reflected in their respective eyes. This shared vision is also provided through the King of Hell. When he was crippled by Hanzō, Nagato developed the Six Paths of Pain technique, a means of controlling six corpses as extensions of himself by embedding them with chakra receivers. Due to sharing his field of vision with the corpses, Nagato could coordinate them with extremely precise planning. He was also able to channel one of the abilities of the Six Paths Technique through each corpse. Obito also applied this technique, though he used reincarnated jinchūriki. Their eyes sported the Sharingan and Rinnegan, in identical fashion to Obito, and their former tailed beasts were temporarily resealed inside them using chakra receivers, though Obito did not have them use the powers of the Six Paths Technique, both to conserve his chakra and because his enemies were already aware of them.

The powers of the Rinnegan remain intact upon being transplanted into another individual, though only Madara has demonstrated the ability to revert his Rinnegan into the Eternal Mangekyō Sharingan. The Rinnegan does not appear to have any noticeable effect on one's chakra reserves, as Nagato wielded it for years unhindered, even in his emaciated state.

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. However, whereas the Rinnegan is depicted as a single shade of purple in the manga, the centre-most ring is depicted as a darker purple in the anime.
 * 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.