Indra Ōtsutsuki

was the creator of ninjutsu and the ancestor of the Uchiha Clan.

Background
In the anime, despite his mother passing shortly after giving birth to his younger brother, Asura, Indra's childhood was peaceful and joyous, spending his time either blissfully alongside his father and brother, or regularly reading his father's books and journals. When old enough, the two began studying under their father Ninshū in the hopes of one of them becoming the great sage's successor. As Indra continued to amaze all with his natural capacities and advanced growth rate, he became showing his ingenious side, realising how chakra could be altered to perform more versatile feats. Soon afterwards, the other Ninshū followers learned from Indra's example and began using this new innovation to improve the quality of life. While initially proud of his discovery, Indra grew concerned when he noticed that everyone began focusing more on physical growth rather than spiritual as what was meant for Ninshū. Periodically, Black Zetsu would approach Indra alone, goading him with praises and curiosity towards Indra's true potential, even going so far as to say he could rival if not surpass the Sage of Six Paths himself. After awakening his Sharingan, Indra began to take to heart the mysterious figure's praises, focusing solely on his training and growing colder to others, including his brother.

When their father was on his deathbed, Asura Ōtsutsuki, Indra's younger brother, was chosen to carry on his dream of establishing peace throughout the world. Indra, jealous that his younger brother was chosen over him, was ultimately manipulated by Black Zetsu into believing that he should have been chosen and chose to fight Asura for it. In doing so, Indra was the first to develop ninjutsu from his father's ninshū. Both brothers died fighting over the title of the successor of Ninshū, but not before having offspring who would continue this feud for centuries to come. Indra's eventual descendants — the Uchiha clan — would feud with Asura's eventual descendants — the Senju clan. Neither clan knew why or how their hatred of the other came to be.

Personality
In the anime, as a young child, Indra was carefree and loving child who looked after and played happily with his younger brother. A very mature boy, he understood the importance of patience and thinking things through. He was very protective of his younger brother and worried about the future of Ninshū when others began to deviate from its original nature following his discovery of chakra transforming. Even after he was revealed as a prodigy, he took other's praises with modesty, only over seeking to help others. He was also very committed to his studies and regular practice.

However, after meeting Black Zetsu and learning more about his true power, Indra realised what his special capacities were capable of and soon revelled in his abilities, proud of being different and expected perfection from himself and others. He became proud and independent, determined to walk his own path unaided. As he did everything with his own power alone, he believed power and force could achieve anything, even peace, an ideology he shared with his grandmother. Despite this, he was able to keep his jealousy of Asura becoming Ninshū's successor in check and held no ill feelings towards his brother and father, who he loved and respected greatly. However, these lingering feelings of rejection from his father allowed Black Zetsu to convince Indra to take the title for himself as it was his birthright, and led Indra to challenge his father's decision. This caused the love Indra had for his father and brother to turn into hatred and wanting the title of Ninshū's leader for himself. Indra's hatred and ideology would have dire consequences for his descendants.

Appearance
Indra had long brown hair cut short on top. Two locks wrapped in bandages framed either side of his face. His eyebrows were cut short — a symbol of his nobility — and dark eyes. Later, he began wearing his hair back in a long cylinder and gained blue markings around his eyes, which were turned up at the corners. He wore a high-collared, light-coloured kimono held closed by a dark sash. The collar of the kimono was adorned with magatama. He wore a black full-bodied suit underneath. When battling Asura, he wore full-body armour, and his hair had been let out to flow around his attire.

Abilities
From a young age, Indra was recognised as a prodigy, even by his legendary father, having inherited much of the latter's power, talent and strong genes. He had a great aptitude for any skill or study he applied himself to. Furthermore, he also inherited his father's "eyes": his powerful chakra, dōjutsu, and spiritual energy. His aptitude was so great, that virtually all of Hagoromo's followers had little doubt Indra would become the his father's successor.

Chakra and Physical Prowess
He was shown highly skilled in taijutsu, with none of his fellow Ninshū students being able to match him in the slightest. Like his father, he had especially powerful chakra and equally large reserves, able to unleash it for a multitude of uses, such as to enhance his strikes. He was also very precise with his chakra manipulation, never wasting more than the absolute minimum for it his techniques.

Ninjutsu
Indra's talents showed an innate capacities for his father's teachings of Ninshū. Ultimately, he learned to expand upon it and single-handedly based a fighting style off it which became known as the true original ninjutsu. In the anime, he could produce multiple clones. He could use Yin Release, and, in the anime, was shown skilled in the usage of Fire and Lightning Release since his childhood. Particularly his skill in Lighting Release enabled him to kill a giant boar with one hit, despite the animal's abnormal strength. He also showed proficiency in a rudimentary form of shurikenjutsu. In later years, he also wielded a sword, showing expertise in kenjutsu.

Dōjutsu
Indra possessed a derived form of his grandmother's dōjutsu; the Sharingan, which he awoken after saving his brother's life. Thus, he could observe the flow of chakra, pay great attention to detail, and accurately predict a person's movements. In time, he also awakened the Mangekyō Sharingan. With it, he unlocked the ability to use Susanoo. Owing to his talent, his mastery over the technique was such that he could use Complete Body — Susanoo, which dwarfed the surrounding landscape. He would use it to combat Asura's own battle avatar.

Legacy
Though his body was destroyed, Indra's chakra would continue to exist. His chakra reincarnated into various individuals throughout history, and his reincarnations would also inherit his will. Indra's desire for his father's title led to centuries of bloodshed and conflict between his and Asura's descendants.

During the Warring States Period, Madara Uchiha was his reincarnation. With his help, Hashirama Senju, the reincarnation of Asura at the time, created the very first ninja village, Konohagakure, and helped set up the contemporary ninja system. However, due to his ambition, insecurity, and Black Zetsu's machinations, Madara defected, and resumed his conflict with Hashirama. After their final fight at the Valley of the End, Madara stole Hashirama's DNA, which he later implanted into his wounds. A portion of Asura's chakra merged with Indra's chakra within Madara, and eventually, he awakened the Rinnegan, something Hagoromo warned against.

When Madara and Hashirama died, the transmigration cycle resumed. Sasuke Uchiha became the latest inheritor of Indra's chakra and will, with Naruto Uzumaki inheriting Asura's chakra and will. Due to the centuries old conflict that arose from Indra's hatred and Hagoromo's decision to anoint Asura, Hagoromo's spirit decided to grant his power to both Naruto and Sasuke when he was able to appear before them. He hoped that the hatred felt by Sasuke would turn into love, and that his sons' reincarnations would be able to work together.

Ultimately, Naruto managed to accomplish what all of the previous reincarnations had failed to do: end the rift between the two lines of the reincarnated brothers. Naruto achieved this after defeating Sasuke, who finally accepted Naruto's ideals at the end of their fight. This brought about the end of the bitter feud that had lasted for centuries. According to Black Zetsu, the reincarnations of Indra and Asura were almost always in conflict with each other and rarely worked together. Naruto and Sasuke are one of the exceptions, assuming other exceptions have existed throughout the centuries.

Trivia

 * "Indra" literally means "King of Gods" in Sanskrit, a possible reference to his obsession with his father's title.
 * The rivalry of Indra and Asura and their descendants (Uchiha and Senju) is derived from Hindu and Buddhist religions where the Gods, led by Indra, are in constant battle against the Asuras. In the teachings, Asuras were malevolent and Indra was benevolent. In the series, however, the brothers' roles were reversed.
 * It is hinted straight tomoe Mangekyō Sharingan are connected to Indra as Madara noted despite its rarity, both he and Sasuke possessed one and correctly speculated they shared some connection beyond blood, as Indra's reincarnations.