Hagoromo Ōtsutsuki

The was a legendary god-like figure who founded the arts of ninjutsu and created the ninja world. He was the son of Princess Kaguya Ōtsutsuki‎‎ and the first human born with chakra. He defeated the Ten-Tails in battle and sealed the beast within his own body, thus becoming the very first jinchūriki.

Background
The Sage was born to Kaguya Ōtsutsuki‎‎, a princess who ate the forbidden fruit of the Shinju, which appeared once a millennium in an effort to gain god-like abilities to put an end to constant wars during that era. As a result, the Sage was born with the ability to manipulate the same type of powerful chakra, which was passed on from his mother. The Shinju, furious with Kaguya's actions, was determined to get its chakra back, which caused the tree to assume a monstrous form of what many christened as the Ten-Tails.

The Ten-Tails rampaged throughout the lands until the Sage managed to single-handedly defeat the beast by becoming its jinchūriki, and became revered as a god for the virtue of his victory. According to the Sannin Jiraiya, the monk with his knowledge of the truth of chakra tried to lead the world to an era of peace instead of conflict. He travelled across the land, spreading his ideal and religion, the, which eventually came to be known as ninjutsu. His great deeds and ultimate desire to bring peace to the war-torn world made him widely known as the.

However, knowing that his death would unleash the Ten-Tails back into the world to continue its rampage and reclaim the chakra that mankind now possesses, the Sage used his Creation of All Things ability to separate the monster's chakra from its body before using before using Chibaku Tensei to seal the husk in what would become the moon. From there, the Sage divided the chakra into nine fragments that are each given a physical form and name. Upon their creation, the newly born tailed beasts were told that they were all still linked to one another despite being separate entities. The Sage also told them that would eventually become one again, yet not as they originally were, and that one shall appear at that time to show them what true power is.

The Sage would leave behind a tablet for his descendants, detailing the history of his struggle with the Ten-Tails. Only those who possess the Rinnegan can fully decipher the contents of the tablet, while a reader with a lesser dōjutsu can still partially interpret the information.

The Sage's ultimate wish was to establish peace across the world, but it was a goal that would never be achieved in a single lifetime. Knowing this, he chose to entrust his strength, dream, and legacy to his two sons. The older son, who inherited the Sage's "eyes" (his powerful chakra and spiritual energy), believed that power was the true key to peace. The younger son, who inherited the Sage's "body" (his powerful life force and physical energy), believed that love was the true key to peace. On his deathbed, the Sage chose his younger son to be his successor. Overcome by bitterness and envy, the older son attacked the younger, beginning a war between them. Their feud has continued on through their descendants: the Senju clan and the Uchiha clan.

Personality
The Sage of the Six Paths was a man who sought peace by spreading his wisdom across the world. He was exceptionally wise, as he was able to bring about a great change to the world by simply disseminating the principles of chakra and his religion. He also seemed to care a great deal for the tailed beasts when they were still with him; he gave them each a name as a sign of their individuality, and told them that no matter how far apart they grew, they would always be together, and would someday be led down the right path. In return, the tailed beasts showed respect and adoration for the Sage. Kurama even shed a tear at the thought of his imminent passing, suggesting that the beasts might even have viewed him as a sort of father-figure.

Appearance
Although initially depicted as a silhouette, several details about the Sage's appearance can be inferred. He had a small and trim goatee and short light-coloured hair that spiked up in the front with two distinctive pieces of hair resembling horns. He wore a white full-length cloak (haori) with a high collar, revealing his necklace with six red magatama. These symbols were later mimicked by Nagato's Deva Path, and the seal around the neck of Naruto Uzumaki's and Minato Namikaze's Nine-Tails Chakra Modes and Tailed Beast Modes. On the back of his cloak was a reflection of a seal which had the Rinnegan with nine magatama (both red in the anime) in three rows beneath it, much like the seal which appeared on Obito Uchiha's back after he became the Ten-Tails' jinchūriki. In one appearance where his face was partially visible, he was in an elderly state.

Abilities
Though not a great deal is known about all the skills the Sage possessed, he is widely accepted to be the most powerful shinobi of all time, having been the only person to defeat the Ten-Tails: a being that was revered as a god, causing the Sage himself to be seen as a god. The Sage was also revered as the man to first understand the very nature of chakra itself. This wisdom, combined with his kekkei genkai, the Rinnegan, allowed the Sage to create the first modern ninjutsu. With such powers at his disposal, the Sage obtained a great following, as men and women from across the world strove to learn from his teachings. As the Sage's disciples grew continuously greater in number, it led to the creation of ninja clans, and later, ninja villages. It is impossible to overestimate the Sage's effect on the course of the ninja world's development. As the first true ninja, he created the ninja world, revolutionised it, and left it forever changed.

The Sage was shown carrying two objects. One was what appeared to be a katana in his hand, whilst the other was a shakujō — a Buddhist ringed staff which is meant to be used in prayer.

Rinnegan
The Sage was believed to have been the only shinobi to have fully mastered the Rinnegan, and also learned to control all five types of nature chakra. He is revered as one of the most legendary figures in the ninja world and was so powerful that he created the moon using Chibaku Tensei on his deathbed. Even Nagato stated that his power paled in comparison to that of the Sage's. As a wielder of the Rinnegan, the Sage also wielded all the abilities of the Six Paths Technique.

Jinchūriki
The Sage developed the first technique capable of sealing a tailed beast inside a human body, making himself the very first jinchūriki in history. Having the Ten-Tails great power contained within him, the Sage developed immeasurable power and chakra that far surpassed all others. Even on his deathbed, the Sage was able to employ his Chibaku Tensei technique on a massive scale and use that chakra to create the moon and seal the body of the Ten-Tails within it, a clear testament to his incredible power.

Yin and Yang Chakra
By using the Yin chakra, that comes from the spiritual energy, and the Yang chakra, that comes from the physical energy, he had the ability to create form from nothingness with a mere thought and then bring it to life. The Sage created the nine tailed beasts from the Ten-Tails' chakra by using this ability.

Treasured Tools
The Sage wielded unique tools which became known as the Treasured Tools of the Sage of the Six Paths, each of which possess a unique and powerful ability, but all of which require a vast reservoir of chakra, which would quickly kill any normal human, in order to be used. Being the jinchūriki of the Ten-Tails, this posed no problem at all for the Sage. The five treasures are: the Bashōsen, Benihisago, Kōkinjō, Shichiseiken, and the Kohaku no Jōhei. By combining the Benihisago, Kōkinjō, and Shichiseiken, the Sage (or any user) can capture the word soul of his victims, and then draw them into the gourd and seal them away. The Bashōsen can generate any of the five basic elements. The Kohaku no Jōhei can seal anyone without the elaborate procedures used for the Benihisago. The five treasures eventually fell into the possession of Kumogakure, and then into the hands of the Gold and Silver Brothers, who made use of the treasures in their criminal activities. Kumo however, managed to retrieve the Kohaku no Jōhei which was kept in the Raikage's office.

Legacy
As time passed, the Sage ultimately faded into legend. His bloodline was divided into the descendants of his two children, which would eventually form the Senju clan — and through distant relations the Uzumaki clan — and the Uchiha clan. As a result of Madara Uchiha acquiring and integrating Senju DNA into his body, the Rinnegan would later resurface. Though he noted nothing happened initially after the DNA integration, when he neared the end of his natural lifespan, the dōjutsu finally awakened. With that, Madara Uchiha managed to undo the Sage's seal on the vessel of the Ten-Tails by summoning it from the moon and formulated the Eye of the Moon Plan to become the Ten-Tails' new jinchūriki.

Because Nagato, a pupil of Jiraiya's, manifested the Rinnegan, the latter suspected Nagato to be the reincarnation of the Sage himself. In reality, Madara secretly transplanted his own Rinnegan to the boy, without his knowledge. Nagato, as a descendant of the Senju-related Uzumaki clan, was the perfect host for the dōjutsu; however, Nagato noted that his own power would have paled in comparison to the Sage's. Others, including Kakashi Hatake, noted that the Rinnegan was viewed merely as a mutation. Kurama and Son Gokū's recognition of the Sage (and the tailed beasts' apparent status as the only survivors from the Sage's lifetime), lends credibility to his existence.

Before he died, the Sage told the young tailed beasts that someone would come and lead them on the right path. The tailed beasts would all later come to agree that this person is Naruto Uzumaki.

Trivia

 * The necklace that the Sage wore might be a reference to the Yasakani Jewel; a legendary magatama necklace that is part of the Japanese Imperial Regalia, together with the Kusanagi Sword and the Yata Mirror.
 * The Sage shares the same nickname with both the First and Third Hokage, who were all known as the.
 * Due to the Gold and Silver Brothers' ability to assimilate Kurama's chakra by eating some of its flesh, the Fourth Raikage suspected them to be distantly related to the Sage.

Quotes

 * (As quoted by Jiraiya)
 * (To the tailed beasts)