Uchiha Itachi
Noted even within the Bingo Book (a list of powerful ninja who have been marked for assassination for various reasons), Uchiha Itachi is an S-Class criminal and a Konoha Nukenin.
Background
He graduated at the top of his Academy class at age 7, had mastered the Sharingan by age 8, became a Chūnin at 10 and was previously an ANBU squad leader at the age of 13.
He left Konoha about five years prior to the setting of Naruto, after slaying his whole clan with the exception of Uchiha Sasuke, his little brother. At 13, he was feared by even Orochimaru. He is now currently associated with Akatsuki. Orochimaru had planned to use Itachi's body as a new container for his soul, but Itachi's power had grown to such a frightening extent that Orochimaru dared not carry out his plan, and decided to leave Akatsuki and try his luck with the younger Sasuke instead.
The reason Itachi killed his clan, and the reason he left only his brother Sasuke alive, still remains unclear. When questioned by Sasuke, he replied "To test my 'utsuwa'." In Japanese, 'utsuwa' (器) can mean "vessel," or "container," but it can also mean "ability," or "tool." Orochimaru uses this word to refer to the bodies he takes over with his Fushi Tensei no Jutsu ("Living Corpse Reincarnation"). In this respect, Itachi's words can mean anything from him having a past connection with Orochimaru, to him simply wanting to test his own power, or to his plans to join Akatsuki and forsake past relations. To make matters even more ambiguous, the first person pronoun Itachi used can also be used as a vulgar second person pronoun. So he could also have meant that he wanted to test Sasuke's 'utsuwa,' although this is unlikely, given his previous remarks about his 'utsuwa'.
He was until recently the only known living person who possessed the Mangekyō Sharingan as revealed in the manga. Itachi has told Sasuke that if Sasuke were to obtain the Mangekyō Sharingan, the people able to use it will total three.
Despite being the murderer of his entire clan as well as his best and closest friend, Itachi is by no means a cold-blooded murderer looking for any excuse to kill someone in his way. When Sarutobi Asuma and Yūhi Kurenai stood between him and the way to his goal (Uzumaki Naruto), he did not kill Kurenai when given the chance, though he did wound her enough for her to remember it; as well as trap her within her own genjutsu. He also could have easily killed Kakashi and Sasuke, but he chose just to torture them with his Mangekyō Sharingan, so they would witness his power.
Currently, Itachi and Kisame are assigned to capture Naruto.
Trivia
- The name "Itachi" means "Weasel". In Japanese mythology, weasels are a bad omen, signifying bad luck and death.
- His favorite food appears to be green and red colored dango (Japanese dumplings) on a stick.
- It is suggested that overuse of the Mangekyō Sharingan has damaged his eyesight as of now. It is unknown if that will affect his fighting ability.