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 Hashirama. 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 his Sharingan.

Years later as the battles between the two clans raged on, Izuna awakened his own Sharingan and became one of the first two Uchiha to awaken the Mangekyō Sharingan. However, during one battle, Izuna was mortally wounded by Tobirama's technique. As Hashirama pleaded with Madara to come to peaceful terms, Izuna told his brother not to listen to their lies.

When Madara later returned to the battlefield, he revealed that the injury inflicted on Izuna was fatal. According to Obito Uchiha years later, the dying Izuna had given Madara his eyes so his brother could obtain the Eternal Mangekyō Sharingan to protect their clan from its growing number of enemies and the Senju. Because of the blindess caused by overuse of a Mangekyō Sharingan, Itachi Uchiha believed that Madara took Izuna's eyes by force to regain his sight.

Personality
Izuna Uchiha was a harmonic and devoted person. He also appeared to be very competitive with his brother, Madara, in terms of skill as they would often spar with one another in an attempt to hone these skills. Izuna looked up to Madara greatly and was even in disbelief when as children, Madara admitted to being weaker than Hashirama. Likewise, Izuna was elated when Madara awakened his Sharingan shortly after. As he grew older, Izuna's love for his clan grew and he fought fiercely to protect it. He soon came to share his clan's opinion regarding the Senju clan, even asking Madara, while severely wounded, not to fall for Hashirama's "false" truce proposals. He looked up to his older brother and was so close to Madara that he even gave him his eyes as a dying gift as a means of ensuring that Madara will be able to better protect the clan's future.

Appearance
Izuna was a fair-skinned man with spiky, 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. As a child, his ponytail was absent, and his hair was spiky in the back, and he wore the standard high-collared robes worn by other Uchiha of the Era of the Warring States with the Uchiha crest on the back, with an armoured chest plate. He sported his hairstyle from his childhood again later in his life as an adult.

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 eyes took the appearance of three bars stretching out of his pupil. When Madara took his eyes, the two Mangekyō combined.

He was also skilled in kenjutsu and was able to fight on par against a young Tobirama Senju.

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.
 * Izuna's eyes had four hosts so far. That are himself, Madara, Nagato and currently Obito, although he has only his left eye.
 * According to the databook(s):
 * Izuna's hobby was training with Madara.