Obito Uchiha

Obito Uchiha was teammates with Kakashi Hatake and Rin under the Fourth Hokage. Obito was frequently late for missions due to the random good deeds he would carry out, which greatly irritated Kakashi. He also seemed to have had a crush on Rin. When Rin is kidnapped during the Kakashi Gaiden arc, Kakashi, the current team leader, insisted that they continue the mission instead of saving her. Citing that those who do not save their teammates are no better than trash, Obito refused and eventually managed to persuade Kakashi to join him. During their rescue effort, Kakashi lost his left eye as a result of an enemy ninja's attack, and Obito awakened his Sharingan to save Kakashi and defeat the ninja. Once finding Rin, Obito again saved Kakashi by pushing him out of the way of a rock slide, though has his right side crushed in the process. Unable to escape with his teammates, Obito had Rin implant his remaining Sharingan eye in Kakashi's damaged eye socket as a gift.

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In chapter 599, it is revealed that Tobi is actually Obito Uchiha who was teammates with Kakashi Hatake and Rin under the Fourth Hokage.

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In chapter 687 Obito died from an Kaguya's attack saving Naruto and Kakashi.