Sasuke Uchiha
Although Obito does not appear for the first time until the series' special chapters focused on his life as a child soldier, he makes a cameo appearance on the cover of the manga's 16th chapter in a picture with Kakashi Hatake. According to Masashi Kishimoto, one of the biggest mysteries in the series' first half was why Kakashi only possessed one Sharingan eye technique (unlike Sasuke Uchiha and other members of the clan, who possessed the technique in both eyes). Kishimoto wrote Kakashi's backstory to show him as a young ninja whom Obito gave his Sharingan when he was nearly killed in a fight. Kishimoto said that by chapter 16 he had conceived a storyline about Obito being an Uchiha and how it would affect Kakashi.