Itachi was born as the eldest son of Fugaku Uchiha, the leader of the Uchiha clan in Konohagakure, nineteen years before the start of the series. He grew up during the Third Shinobi World War and became a pacifist due to what he saw then. Itachi grew to be the pride of the clan, graduating from the academy after one year, mastering Sharingan by the time he was eight, becoming a Chunnin at ten, joining the Anbu a six months later, and becoming an Anbu captain at age thirteen. When the Uchiha clan plotted a coup to take over Konohagakure, Itachi, who was to be their go-to, betrayed them, knowing that if they were to revolt, many innocents would die and another world war could start if Konoha's enemies were to invade on the civil war that would happen in Konoha should the coup be attempted, and supplied the village with information on the Uchiha, later buying time for the matter to be resolved. He also secretly made a deal with Danzo Shimura, one of the elders, who lied to him and promised to spare Sasuke Uchiha, Itachi beloved little brother, if Itachi would wipe out the rest of the clan should Hiruzen Sarutobi, the Third Hokage, fail to end their coup. After Hiruzen eventually failed to resolve the matter peacefully, the elders of Konoha ordered Itachi to wipe out the Uchiha clan. He and Tobi, whom Itachi had met prior, wiped out the Uchiha, sparing only Sasuke. Not wanting Sasuke to hate their clan, Itachi lied to him about why he did this deed and said he was sparing Sasuke only for a hoped, future fight. He, however, really spared Sasuke because he was too young to take part in the uprising and therefore had no knowledge of it and was innocent, and because Itachi loved Sasuke too much to kill him anyway. Itachi left the village and joined the Akatsuki as a spy after Hiruzen promised to protect Sasuke when Itachi saw through Danzo's deception about promising to let him live. Itachi, however, also threatened Danzo that if he dared to harm Sasuke, Itachi would reveal everything he knew of Danzo and Konoha's secrets to enemy countries in order to ensure his brother would live to kill him, wanting to make him a hero when he did. Not long after he joined the criminal organization, Orochimaru, one of the Sannin who was a member, tried to steal his body for himself, with Itachi managing to catch him in a genjutsu thanks to his lack of awareness of the lengths of his prowess in the area, and cutting off his hand in retaliation. At some point, Itachi caught a fatal disease, and began to use medication to prolong his life to stay alive long enough to let Sasuke kill him in the future.
In part 1, Itachi first appeared in Konohagakure again after the death of the Third Hokage to warn Danzo Shimura that he was alive and not to harm Sasuke under the cover that he was looking for Naruto Uzumaki. After giving Danzo his warning, Itachi and his partner, Kisame, continued to search for Naruto, the host of the Nine-Tailed Demon Fox, overwhelming Kurenai Yuhi and Asuma Sarutobi, two jonin of the village, before Kakashi Hatake arrived as backup. Itachi faced and defeated Kakashi with his Tsukuyomi, before they left after Might Guy arrived, not wanting to fight a full-on battle. After finding Naruto in the company of Jiraiya, one of the Sannin, Itachi and Kisame realized they would die if they fought him, so Itachi used a genjutsu on a pretty, young woman to distract Jiraiya. When they confronted Naruto, Sasuke, Itachi's younger brother, found them, and Itachi overpowered him, before Jiraiya arrived, having released the genjutsu on the woman, and declared he would kill them both. However, he let Sasuke fight Itachi, who defeated him with Tsukuyomi to drive his desire to kill him further, before Jiraiya used his Summoning: Toad Mouth Bind to entrap Itachi and Kisame. They were nearly killed by it, with Itachi being forced to use Amaterasu to break them free, and they fled, failing to capture Naruto.
In part 2, Itachi first appeared to keep Team Kakashi and Chiyo, an elder of Sunagakure, busy by manipulating a specially-made clone created by the Akasuki's leader, Pain, that had 30% of Itachi's chakra while he and the rest of the Akatsuki finished removing and sealing the One-Tailed Shukaku out of Gaara, but it was defeated. However, they still managed to complete the sealing of the beast before the hide-out was reached. Before he deactivated his silhouette, Itachi described Naruto Uzumaki's personality to Deidara.
Later, while being searched for, Itachi met with Naruto again, this time to just talk, though he had to catch him in a genjutsu to convince him so. After asking Naruto why he cared for his brother, who abandoned the village willingly and betrayed it, so much and, after hearing his answer, gave him some of his power to be used on Sasuke should he attack Konohagakure, praying that he would never have to use it, leaving afterwards. Using a crow clone to point Sasuke to his location, Itachi later met with younger brother at the Uchiha hide-out. Their final battle started off with them engaging in a genjutsu fight, in which Itachi revealed to Sasuke that Obito Uchiha(Itachi believed he was Madara Uchiha) was his accomplice in the Uchiha clan massacre. Itachi caught Sasuke in his Tsukuyomi, which Sasuke broke out of, making the genjutsu fight pointless. Afterwards, Itachi's left thigh was wounded by Sasuke, who then used his Fire Release: Great Fireball Technique and Chidori to drive Itachi outside. As they collided the Fire Release attacks, Itachi's began to be overpowered, and he used his Amaterasu to counter Sasuke. Managing to strike him after a couple of misses with the black flames, Itachi was surprised when it turned out Sasuke used Orochimaru's power to shed his body and slip away into the room below. He was then hit by another Fire Release attack from Sasuke that, along with the black flames of Amaterasu that had missed Sasuke, caused a powerful thunderstorm to form. When Sasuke utilized his Kirin technique, Itachi, having yet to remove Orochimaru from within Sasuke, was forced to use his Susanoo to live through the attack. After Orochimaru took his presence on the battlefield quickly thereafter, Itachi stabbed him with the Sword of Totsuka and sealed him in Susanoo's goard.
With Sasuke tremendously weakened, Itachi, as he cornered Sasuke, appeared to reach for his eyes, but instead poked his brother's forehead and sealed the Amaterasu in him to be used against Obito should he approach Sasuke, before finally dying with a smile and collapsing dead. He was later revived by Kabuto Yakushi during the Fourth Shinobi World War, along with the other deceased Akatsuki members as a military weapon, being paired up with Nagato. Under Kabuto's direction, they eventually encountered Naruto Uzumaki and Killer B, the Eight-Tails, Gyuki's jinchuriki, with Itachi expresssing surprise that the latter had gained his Nine-Tails Chakra Mode. Under Kabuto's direction, Itachi and Nagato were forced to battle Naruto and B. As he clashed with Naruto and B, Itachi asked the former what happened to Sasuke, becoming shocked to learn he had found out the truth about him from Obito, who he never knew completely was aware of the truth about him. After Naruto began to reveal the truth about the Uchiha clan massacre openly, Itachi, after Nagato asked him if it was all true, told Naruto to be quite. The conversation didn't go very far, as Nagato and Itachi were soon forced to keep fighting, Nagato against Naruto, and Itachi against B. Catching B in a genjutsu, Itachi warned him not to look at his eyes, as he was about to be forced to use Tsukuyomi. However, Gyuki, the Eight-Tails, quickly broke B out of the genjutsu, before that and Itachi then forced to retreat from B's Seven Swords Dance, not being able to read it.
After jumping up on the head of Nagato's giant bird summon, Itachi activated his Mangekyo Sharingan, causing a crow to emerge from within Naruto(this was the sample of his power he gave him to be used against Sasuke if he should attack the village). This crow, having Itachi's long dead friend, Shisui Uchiha's, Mangekyo Sharingan, then cast the genjutsu Kotoamatsukami on Itachi, allowing him to override Kabuto's control. Itachi then hit both Nagato and his bird summon with the Amaterasu, afterwards explaining how he was able to gain control of himself again, and why he had given the crow and its eye to Naruto instead of using it on Sasuke himself. However, Nagato repelled the black flames off of him and overpowered both B and Naruto when they engaged him. before they could be killed, Itachi used his Susanoo to save the two, and Nagato quickly began to use his Chibaku Tensei to create a giant orb to defeat them all, but Itachi devised that they each use their strongest individual techniques to counter, managing to destroy it. Itachi then impaled Nagato with his Sword of Totsuka, telling him to impart any final words he ad as he sealed him away permanently. Advising Naruto after he began to express belief that it was his duty to stop the war alone that that would only cause him to become arrogant, like Obito, and that he should rely on his friends, a fact Itachi knew all too well from having tried to handle Sasuke and steer him right on his own, and failed in doing so. Afterwards, telling B to look after Naruto, Itachi left to end the Kabuto's Impure World Reincarnation.
Later, he encountered Sasuke, much to the latter's surprise, and was chased after by him, conversing with Sasuke after he countered his Susanoo with his own. After telling Sasuke he had soared him in the past because of his innocence ans his own personal desire to be judged by an Uchiha for his actions(also he did so out of love for his brother), Itachi decided not to speak to him anymore, having turned him into a criminal with his past decisions, and that he would leave it to Naruto to change him. After telling him he had to stop Kabuto's technique after his brother claimed that even in death, he was still running away from him, Itachi tried to throw Sasuke off by summoning a flock of crows to obscure his vision. Smashing through the wall where Kabuto was hiding, Itachi came to feel rather awkward after the latter revealed his technique would not end, even if he was killed, and that only he could stop it. Sasuke arrived quickly and, while Kabuto tried to trick him into fighting Itachi, Sasuke responded that he had only followed his brother to talk to him. Itachi then agreed to talk to sasuke after they had defeated Kabuto and ended his technique, and the two engaged Kabuto together. During the long battle that followed, Sasuke and Itachi, despite their immense battle prowesses, were continously overwhelmed by Kabuto, who had mastered not only Sage Mode, but the powers of Orochimaru, the Sound Five, and most of Sasuke's team, Taka. Itachi was nearly put back under Kabuto's control once, being saved by Sasuke in time, and he, after being overpowered enough, decided to use the forbidden technique, Izanami, the partner technique of Izanagi, becoming impressed when Sasuke revealed he had defeated Danzo Shimura while he was using it. After the battle progressed some more, Itachi told Sasuke to stay close, as Izanami would now begin, which paralyzed Kabuto physically, and trapped his mind in an infinite memory loop of replaying events of the fight, telling Kabuto he must accept his mistakes to break out of it
As Itachi moved to end the Impure World Reincarnation, Sasuke seemed shocked as that mean't he would vanish too, but Itachi stated he had no further purpose in this world and that he was happy to be able to protect Konohagakure one last time. This angered Sasuke, who wanted to know why he was so willing to help the village that had used him so and arguing that Itachi was the one who had made him the way he is. Itachi, however, only replied that he was not the one who could change Sasuke now, and that that was why this was the least he could do to keep from ruining what he had left in Naruto's hands. Itachi then put Kabuto under genjutsu and forced him to tell him the seals to end his technique and had him execute its release. As he slowly began to lose his consciousness, Itachi told Sasuke that what Danzo and Obito had told him was true, and put him under a genjutsu to show him everything happened prior to the massacre of the clan. After this, Itachi approached Sasuke and, admitting his past mistakes, told him, as he touched their foreheads together, that, regardless of the paths he chose from then on, he would always love him, as his soul emerged from its shell and returned to the afterlife.
Itachi at first appeared to be very evil and cruel, but was truly a very kind and loving ninja, who betrayed his clan out of love for his village and would not kill his little brother, who he loved even more than Konohagakure. Itachi also dearly loved his parents as can be seen when he spared them until last out of the Uchiha on the night of the massacre and was brought to tears and shook tremedously before he killed them. Itachi was a very pacifist man, and usually did not take part in battle, only fighting when he had too and usually in self-defense. He was one of the few Akasuki members who got along well with their partners, having a good friendship with Kisame Hoshigaki. Itachi was always careful not to underestimate his opponents, shown in his praise of Jiraiya, saying on his own he wouold be no match for the Sannin, and that, even if he had his partner, Kisame, by his side, the best of their combined efforts against Jiraiya would end in a stalemate. He also had great emotion control and kept his composure even when surprised. Itachi had a quite sense of pride in his power, but once acted very arrogantly towards Deidara, shown when he first met him.
Itachi was an extremely powerful shinobi, shown in his ability to easily defeat other immensely powerful shinobi, such as Kakashi Hatake, and his fellow Akatsuki, Deidara. He was also able to defeat the extremely powerful Kabuto Yakushi with just one very powerful genjutsu, though the latter had previously overwhelmed both him and his brother, Sasuke Uchiha's combined efforts and forced him to do so. He was also able to catch Orochimaru, one of the Sannin, off-guard on both the occasions they met, cutting off his hand the first time and sealing him away with the Sword of Totsuka the second. However, fairly, Itachi was only able to do these things because Orochimaru lacked awareness of certain details each time, and Itachi still didn't manage to seal him away permenantly as he believed he did. Even when he was only an academy student, Itachi was hailed by his teachers as a natural genius and graduated in just one year. His natural talent allowed him become a Chunin at age 10, and six months later he joined the Anbu, becoming an Anbu captain at age thirteen. In life, Itachi was the strongest member of the Uchiha clan out of his generation, and was able to, with assistance from Obito Uchiha, slay every member of his clan when they decided to try and stage an uprising against Konohagakure. His power was great enough that, at this point, he was able to become a member of the Akatsuki, a criminal organization of S-rank missing-nin.
As an Uchiha, Itachi was a master and true heir of the Sharingan, which he managed to master at a young age, but not as young as his ancestor, Madara Uchiha. It allowed him to see chakra, predict his opponents moves and foresee their attacks, copy most enemy techniques, and use formidable genjutsu. He first became able to use it when he was 8 and, amoung other things, was praised, alongside his best friend, Shisui Uchiha, as the Uchiha, of modern times, most gifted in the use of the Sharingan's visual genjutsu. With this prowess, Itachi was able to easily outmatch and defeat Kurenai Yuhi, a Jonin of Konohagakure and genjutsu specialist, using a genjutsu reflection, ending their confrontation after it barely had started. Itachi's mastery of the Sharingan was so much, he became able to easily use the forbidden dojutsu, Izanami, the partner technique of Izanagi, which he was able defeat Kabuto with after a long fight. Not all of his genjutsu were of the Sharingan, but all of them were potent, as even a normal one was too much for Naruto Uzumaki to break himself out of, despite having to been trained to do so by Jiraiya, one of the Sannin. Itachi was such a master of genjutsu that all he needed to do was point a single finger to catch someone in a powerful genjutsu, such as the one he caught Naruto in. Also as an Uchiha, Itachi was very skilled in the use of Fire Release techniques, having mastered his clan's signature technique, the Great Fireball Technique, after only one try, which allowed him to build up his chakra in his chest and exhale it in the shape of the of a large fireball. His mastery of this technique was such that Samehada, the sword of his partner, Kisame Hoshigaki, which devours chakra, was bothered by its flames when Killer B used it to cut through them. He was also able to use the Fire Release: Phoenix Sage Fire Technique to exhale a barrage of smaller fireballs at great speed, which were difficult to dodge. Itachi could also use Water Release to create swirling funnels of water from any given source, which he could use to deal great damage to an opponent not capable of countering him. As an Uchiha, Itachi was also quite skilled in the use of various weapons, such as shuriken, kunai, and, as an Anbu, swords. His brother, Sasuke, openly noted that out of all the Uchiha, Itachi was the best in the use of shuriken, more than even their father, Fugaku, the clan leader. This was evident when, even when in a near-blind state, Itachi was to easily counter all of Sasuke's shuriken in their last fight, and still be able to make a shadow clone at the same time.
Itachi was one of the few Uchiha, others before him being his best friend, Shisui, and his ancestors Madara and his brother, Izuna, to awaken the Mangekyo Sharingan. This allowed Itachi to use some of his strongest techniques and genjutsu, such as Tsukuyomi, which allowed him to trap his opponents in a genjutsu world where their time perception would become extremely warped, and wherein he could torture them for up to what appeared to be three days, but in reality was just one second. This technique laid Kakashi Hatake, a Jonin of Konohagakure in a coma for over a month after he used it on him. According to Itachi, only someone with both a Sharingan and kekkei genkai could break his Tsukuyomi, however, this was not correct as a jinchuriki with a partnership with their tailed beast or with full control over it can break any genjutsu, even Tsukuyomi, through their tailed beast by having them break it for them. Nevertheless, Itachi's prowess and mastery of Tsukuyomi was so great, that Danzo Shimura openly stated that his younger brother, Sasuke's genjutsu was a far cry from Itachi's. Itachi could also make use of the strongest fire technique in existence, Amaterasu, which creates blacks flames as hot as the sun that are said to be unavoidable and able to burn through anything. Again, just like with Tsukuyomi, these claims have been proven incorrect, as Sasuke was able to avoid the black flames twice before being hit by them, which happened only because Itachi began to guide them with his eye. A, the Fourth Raikage, was also able to easily avoid these flames while battling Sasuke by use of his Lightning Release Amor at full power, combined with the Body Flicker Technique.
Though Amaterasu's flames have normally not failed to burn through something, they were ineffective against Gaara's Shield of Sand, which not only outran them, but also blocked them perfectly, without being burned through or even into. Itachi's greatest technique of the Mangekyo Sharingan was his Susanoo, which created an immense, ethereal warrior around Itachi capable of weilding the spiritual weapons, the Sword of Totsuka and the Yata Mirror. The Sword of Totsuka was imbued with sealing techniques and capable of sealing away anything it stabbed into Susanoo's goard in a genjutsu state of drunken dreams for all eternity. Using this ability, Itachi was able to seal away Orochimaru, though not forever and would not have at all if he had known what the weapon was. The Yata Mirror was capable of repelling both any elemental chakra attacks and physical attacks, and was noted by Zetsu, an Akatsuki member, to have, along with the Sword of Totsuka, made Itachi nearly invincible when he used Susanoo. Along with these impressive weapons, Susanoo itself is a remarkable defense, but it is not absolute as in saving Itachi from Sasuke's Kirin technique, it was completely destroyed, despite being in its complete form. Itachi also showed great skill in sealing techniques, able to seal his Amaterasu as a trap for Obito Uchiha in Sasuke's left eye to keep the former from telling the latter the truth about him, though this ploy failed. Obito did, however, praised Itachi's ability to plan ahead and set a postmortem trap, despite being seconds from death at the time.
Despite it not being a prefered method of combat, Itachi was very skilled in taijutsu, able to easily defeat three members of the Uchiha clan, all of them his senoirs, with just single attacks, and outmatch and overpower Sasuke at their first reunion with great ease, despite the latter's mastery of strong fist and extensive taijutsu training during the Chunin Exams. He was also able to hold his own against both Naruto and Killer B after his revival individually, though was forced to retreat when fighting them both. He was able to keep up with B's Seven Swords Dance and evade it, though was not able to fight it and reduced to only dodging capability, whereas Sasuke before him had been easily overwhelmed and critically wounded by B when he used against him. In the anime, Itachi was strong enough to kick the ground and cause small craters to appear from the sheer force of his strikes.