Uchiha Izuna
Izuna was the younger brother of Uchiha Madara. He helped lead the Uchiha clan alongside his brother around 70 years before the series start.
When they were young, Madara and his younger brother Izuna competed against each other. Both possessed the Sharingan and attained Mangekyou through their rivalry. With their newfound power, they increased their clan's power and standing. Unfortunately, usage of Mangekyou leads one to blindness and Madara was the first to fall to this side effect. With his eyesight gone, Madara took Izuna's eyes in desperation. These new eyes allowed him to see once again and granted him "Eternal" Mangekyou.