Obito Uchiha

Obito Uchiha was one of Kakashi's teammates in the manga exclusive Kakashi Gaiden. He was a 13-year old Chunin in Team Minato with Kakashi, Rin, which was led by Minato Namikaze (the future Fourth Hokage). He's very similar to Naruto Uzumaki, goofy and desperate to prove he is a worthy ninja, mostly unrespected by peers and teachers alike. However, he is ready to put his life on the line for his teammates without hesitation. Obito carries the blood of the Uchiha Clan and has the power of the Sharingan within him.

Kakashi Gaiden arc
Obito was first seen desperately rushing to meet with his team, but arrived late and got scolded by Kakashi. Minato then states that as Kakashi is a Jonin, he will be in charge of Rin and Obito, while he did missions by himself. Rin then reminded Obito that he needed a gift for Kakashi, but while he did not have one, Kakashi suggested that Obito would give him something worthless if he did. The group then received their mission to destroy a supply bridge to prevent a Rock village ninja invasion of the Land of Grass.

During the group's first encounter, Obito froze up in the heat of battle, prompting Minato to bring him to his senses. After Minato killed the enemy ninja and told Kakashi that teamwork was more important than the rules, Obito tried to rub it in, but was told that he needed to control himself in order to back up his words. Obito, again feeling inadequate, talked with Minato about Kakashi and learned his story.

The next day, Minato temporarely left the group for an urgent mission, thus leaving Kakashi, Rin, and Obito by themselves. Two Rock ninja tried to ambushed the team, causing Rin to be kidnapped. Kakashi argued that the mission came first, as diverting to save Rin would compromise it, but Obito argued that Rin was their friend, and they needed to save her. Obito then left, stating that while those who break the rules are trash, those who abandon their friends are worse than trash.

Shortly after Obito reached the location where Rin was held, a Rock Village ninja began to attack Obito from behind, but Kakashi stepped in just at the nick of time to save him. The ninja hid himself, and Kakashi lost his left eye saving Obito from an attack. Obito realized that the time had come for him to live up to his words, and activated his Sharingan for the first time. He saw and killed the ninja who attacked them both. After the two saved Rin, a third Rock Village Ninja caused a cave-in, and Obito was trapped under several rocks while saving Kakashi. The whole right side of his body was crushed, slowly killing him. When Kakashi went to his fallen teammate's side, in confirmation of their friendship and as a gift for Kakashi gaining Jonin rank (Obito was the only member of the team not to have given Kakashi a gift), Obito gave Kakashi his left eye, and the Sharingan with it. Along with the quote " I'm already going to die, but I can become your eye. And from now on I will see the future". After Kakashi defeated the ninja, the cave collapsed as enemy reinforcements arrived, and Obito died, realizing that he had finally become friends with Kakashi. Though he was unable to tell Rin how he felt about her.

Personality
Kakashi's trend of being late seems to have come from Obito. He was almost always late, and was carefree about rules, leading to a rough relationship between himself and Kakashi. While Kakashi believed that the rules were everything during his time with Obito, Obito believed that self-control and caring for one's friends was more important. Despite his carefree appearance, Obito often suffered from self-doubt, as while he boasted that he would surpass Kakashi once his Sharingan awakened, he later stated that he saw himself as a "washout" among the Uchihas. Obito had romantic feelings for Rin, but never was able to confess them to her.

Appearance
Obito wore a ski mask-like pair of goggles with a see-through orange tint (the goggles have no color in the anime). He also wore dark blue pants and a jacket. His hair was spiky like Naruto's, but was a black color.

Trivia

 * Obito graduated from the Academy at the age of 9, he also got promoted to Chunin at the age of 11.
 * Kakashi's famous quote: "Those who break the rules are scum, but those who don't help a comrade in need are worse than scum." (English dub version) was actually Obito's original quote.
 * Kakashi's always late because he spends too much time at Obito's grave, honoring him after the Uchiha died.
 * When recommended that he should wake up earlier to honor Obito (thus getting more time to do important things) by Yugao Uzuki, Kakashi replies that if he comes by earlier, he will stay longer thinking about his regrets.
 * Many people believed Obito was posing as Tobi, since Tobi's mask showed only the Sharingan of the right eye, and Kakashi has the left. But then it's reavealed that Tobi is Madara Uchiha.