Uchiha Obito

Obito is a genin level ninja featured in the Kakashi Gaiden chapters of the Naruto manga. Obito wants to prove his strength to Kakashi, who is his team mate and his biggest rival. Obito also has a crush on his other team mate, Rin. On his and Kakashi's mission to rescue Rin, Obito finnaly proved his strength to Kakashi by activating the Uchiha clan's special ability, the Sharingan. When all seemed to be going well a rock ninja used a rocklisde jutsu and smashed Obito, completely crushing the right side of his body. Obito, knowing that he was going to die, offered his sharingan to Kakashi, so he could defeat the rock ninja and save Rin. Rin, being a medical ninja, implanted Obito's left eye into Kakashi's left eye socket. This is the origin of Hatake Kakashi's sharingan eye.