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
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. When Madara eventually went blind, 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. Izuna later died honourably in battle, fighting to the death even in his blind state.

Personality
Izuna Uchiha was a harmonic and devoted person. He also appeared to be very competitive with his brother, Madara, in terms of skill. Tobi 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. Izuna's loss of his eyes rendered him blind, but he managed to survive, and continued to battle. This sudden disability however, ultimately led to his death.

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 so he could stay 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.
 * According to the databook(s):
 * Izuna's hobby was to train with Madara.
 * Izuna's eyes have been transplanted into 3 different people over a period of 80 years. First to possess them was Izuna himself, until they were transplanted into his brother Madara Uchiha. After awakening the Rinnegan, Madara Uchiha transplanted Izuna's eyes into an infant Nagato. After his death, Izuna's eyes were stolen from Nagato's corpse to be transplanted by Obito Uchiha into himself.