At the age of 7 he had graduated from the top of his class in nin-academy of Konohagakure. At 8, he mastered his Sharingan eye and, at ten, became a Chunin. He became the leader of his own Anbu squad at 13. Because of these accomplishment, the Uchiha clan (especially his father) believed that he was the future of the clan. This made his father focus most of his attention on Itachi, and Itachi's brother, Sasuke, was neglected. Itachi began saying that he would train with Sasuke, but he was forced by his missions to break his promise. He did, however, make his father send more time with Sasuke by refusing to do missions unless his father went along.
Six months after Itachi became an Anbu squad leader, Itachi began losing ground with the clan. He began to neglect his missions, and was a prime susect in his best friends death (his best friend had apparently committed suicide, but it was questioned by the clan elders). When a band of invesigators confronted him, he easily defeated them, saying that he had lost faith in the clan. He later apologized at his father's bidding. Itachi's father then began spending more time with Sasuke, trying to steer him away from Itachi's path.
Itachi later killed his entire clan, with the exception of Sasuke, and gave his reason as "testing [his] limit." He then told Sasuke to beome strong enouh to kill him, and toldhim how to gain the Mangyekou Sharingan: killing your closest friend.
Itachi, at some point, joined Akatsuki, and when Orochimaru attempted to defect and steal Itachi's body, Itachi disabled him and severed his left hand and forced Orochimaru to flee.
Itachi later reappeared in Konohagakure in an attempt to capture Naruto. In his first appearance, he defeated Kurenai and Kakashi without a single wound. He was going to capture Kakashi, who knew about Akatsuki, but Guy's timely intervention made this impossible. He later came face to face with Sasuke, who attempted to kill him with Chidori. Itachi easily blocked it and kicked Sasuke back down the hall. On this occasion, Itachi was forced to retreat because of Jiraiya's intervention.
Later, in part two, Itachi fought the team 7 when they attempted to retrieve a captured Gaara. Naruto was able to defeat him with Great Sphere Ransengan, only to discover that Itachi was not Itachi, but an imposter created by the Akatsuki Leader.
Presently, Itachi is being targeted by Naruto, Kiba, Shino, Sakura, Sai, Yamato, Kakashi, Hinata, Sasuke, Juugo, Suigetsu, and Karin.
After Sasuke's supposed death at the hands of Deidara, Itachi appeared to be crying in the rain, but when Kisame commented on this, and the fact that Sasuke's death would make him the last member of the Uchiha Clan, Itachi stated that Sasuke was not dead, and that the storm had passed.
Naruto, following a bird covered in Sasuke's scent, Hid in a tree as he saw Sharingan, beliving them to belong to Sasuke, but they were revealed to be Itachi's, and he ordered Naruto to come down from the tree he was hiding in.