Izuna Uchiha

was a shinobi of the Uchiha clan. He along with his brother Madara Uchiha were renowned as the clan's two strongest members.

Background
As a child growing up during the war-torn era, Izuna once accompanied his father on a mission to kill Hashirama Senju whom Madara, albeit unknowingly, had been meeting. Once there, Izuna and his father were confronted by Butsuma and Tobirama Senju, the latter of whom he acknowledged by name.

As Izuna clashed with Tobirama, unbeknownst to him, Butsuma had launched an attack at him, hoping to strike him down and gain an advantage at defeating the evenly-matched Tajima. This attack, however, was deflected by his brother Madara who had intervened between the two sides along with Madara. Izuna later showed shock when Madara noted that Hashirama was stronger than he was, but was later elated to see that his brother had awakened the Sharingan. Years later as the battles between the two clans waged on, Izuna was mortally wounded by Tobirama's technique. As Hashirama plead with Madara to come to peaceful terms, Izuna told his brother not to listen to their lies. Madara would later return to the battlefield, without his brother, noting that Tobirama's attack had been fatal. Now wielding the Eternal Mangekyō Sharingan — the strength he noted that he received from his brother — Madara was nonetheless defeated by the Senju, and it was there that Madara told Hashirama that he no longer had any siblings, nor trust for the Senju and the only way to regain it, was to either kill himself, or Tobirama.

Eighty years prior to the start of the series, Izuna and his older brother Madara were said to be equals as the most gifted members of the Uchiha clan. They usually competed with each other every day in order to get stronger. Both awakened their Sharingan early in life, and they became the first Uchiha to awaken the Mangekyō Sharingan. Madara used the power of his Mangekyō Sharingan to take control of the clan, with Izuna at his side. It said that Madara became blind, and he took Izuna's eyes to regain his sight. Itachi Uchiha suggested that his eyes had been taken by force, however Tobi insisted that Izuna had willingly given up his eyes for the good of his brother and the whole clan, seeing that Madara needed to remain strong to protect the clan from its growing number of enemies. In reality, Izuna died with the mortal wound Tobirama had inflicted on him. Before he died Izuna gave his eyes to his brother and it granted Madara an Eternal Mangekyō Sharingan. Madara's love for his brother lends credibility that Izuna willingly allowed Madara to take his eyes.

Personality
Izuna Uchiha was a harmonic and devoted person. He also appeared to be very competitive with his brother, Madara, in terms of skill. Obito also implies that Madara and Izuna were close as brothers.

Appearance
Izuna was a fair-skinned man with long, black hair that had a blue tint to it and was tied in a ponytail. His bangs parted down the centre of his face to frame both sides of it. He wore the standard Uchiha outfit which consisted of a high-collared, blue shirt with the Uchiha Crest on his upper back and blue pants which were wrapped up in bandages at the ends. On his waist, he had a bandage belt that held a sack which presumably held ninja tools.

Abilities
Izuna was noted to be equal to his elder brother, Madara, in every way. Both of them had exceptionally strong chakra, even for Uchiha members, and trained daily to hone their skills. Izuna mastered his Sharingan at a very young age, alongside Madara. When Izuna awakened the Mangekyō Sharingan, his took the appearance of three bars stretching out of his pupil. When Madara took his eyes, the two Mangekyō combined.

He was also seemingly skilled in kenjutsu after being observed on the battlefield as a child with a sword in his possession.

Legacy
While posing as Madara, Obito Uchiha claimed that Izuna's death after giving Madara his eyes played a great role in Madara's antagonism towards the Senju clan when they proposed a truce. Madara would have thought Izuna's sacrifice to keep him strong and protect the clan as being in vain. Izuna's eyes continued to be of great importance, first, by granting Madara the Eternal Mangekyō Sharingan, and in his old age, Madara would also awaken the Rinnegan with Izuna's eyes. The same eyes were later transplanted into Nagato, who would later go on to become Pain, and a powerful figure-head of Akatsuki, and then into Obito Uchiha, who came to share Madara's ideals, and while posing as him, plunged the world into the Fourth Shinobi World War.

Trivia

 * is the name of a fox spirit in Japan and of a mountain. The latter is usually called Mount Iizuna, though. Iizuna, written with the same kanji, is also the Japanese name for the least weasel. Izuna's name can also be from a mythical god and wind spirit named Izuna that presents himself in the form of a tengu, which may be a reference to Susanoo's perfect form that resembles a tengu.
 * Izuna and Obito share the same birthday, and blood type.
 * According to the databook(s):
 * Izuna's hobby was training with Madara.