Kisame Hoshigaki was an S-rank Missing-nin from Kirigakure and one of Akatsuki's most powerful members. Prior to defecting from his village, he was one of the most powerful gerneration of the Seven Ninja Swordsmen of the Mist's members. He was partnered with Itachi Uchiha.
Kisame was born into the village of Kirigakure, where he became an elite and, at first, loyal shinobi. His mentor was a member of the Seven Ninja Swordsmen of the Mist, and on one mission, as Kisame's team found themselves pursued by a squad of Konohagakure shinobi led by Ibiki Morino, Kisame killed all of his teammates to keep them from being captured and tortured into revealing information. Managing to evade capture himself, Kisame reported back to his master who Kisame, knowing he had betrayed the village by selling information to other shinobi villages, killed and took possession of his sword, Samehada, taking his place as a member of the Seven Ninja Swordsmen. Though praised by the Fourth Mizukage, Yagura, Kisame saw these actions of his as him becoming a "living lie". He later came to discover that the Mizukage was being controlled by a strange shinobi who called himself Madara Uchiha(really Obito Uchiha, Madara's apprentice), who told Kisame of his Eye of the Moon Plan. Though Kisame initially thought him insane, the concept of the plan to reveal a "world of truth" appealed to Kisame, and he defected from Kirigakure and became one of the first and most loyal members of Akatsuki, a criminal organization Obito ran(from the shadows, as Pain was public leader of the group), afterwards becoming an S-rank Missing-nin. Kisame was partnered with Itachi Uchiha due to knowing about him, and while they initially were hostile to each other, they later became great friends and partners. At some point, Kisame also became affiliated with Suigetsu and Mangeksu Hozuki, of Kirigakure's Hozuki clan.
Kisame made his debut in part 1 of the series, alongside his partner, Itachi Uchiha, travelling to the latter's home village, Konohagakure, to capture Naruto Uzumaki, the jinchuriki of Kurama, the Nine-Tails. They were confronted by Asuma Sarutobi and Kurenai Yuhi, two Jonin of the village who demanded their names. A fight soon ensued, with Kisame easily overpowering Asuma, before Kakashi Hatake arrived as back up. Though Itachi defeated him easily, when Kisame attempted to kill the rest and take Kakashi hostage, Might Guy, another Konoha jonin, arrived and kicked Kisame away. They then fled, rather than risk an all-out battle. They found Naruto in the company of [[Jiraiya], one of the legendary Sannin, who Kisame felt inferior to. As they didn't want to risk a fight with the Sannin, Itachi cast a genjutsu on a pretty woman to lure away Jiraiya, before the two confronted Naruto. Not long thereafter, Itachi's brother, Sasuke Uchiha arrived to kill him. After Itachi outmatched him, Kisame tried to cut off Naruto arms to disable his techniques, though Jiraiya then arrived and countered him, having seen through their ploy. Though Itachi went on to defeat Sasuke, when Kisame attempted to stop Naruto from aiding him, Jiraiya entrapped him and his partner in his Toad Mouth Bind technique and drove them away. Though Kisame and Itacho were nearly killed, the latter used his Amaterasu technique and allowed them to escape, and they failed to capture Naruto.
In part 2, Kisame made his debut sealing the One-Tailed Shukaku from within Gaara, though he was forced to send a clone with 30% of his chakra to battle Team Guy. Though he overwhelmed Might Guy's students easily and fought with Guy on even terms, the clone was defeated when Guy opened six of the inner Eight Gates and used his Morning Peacock technique to fight back. Kisame and the others, however, still managed to seal Shumamu in time. Later, Kisame helped to seal the Two-Tails, Matatabi and the Three-Tails, Isobu, when they were captured(in the anime they were done one after the other, though in the manga, the Three-Tails was done first and much earlier). Kisame went on to defeat and capture the Four-Tails jinchuriki, Roshi, on his own and helped to seal him, being informed later that Deidara had died fighting Sasuke, but that the latter had also died. Informed of the opposite by Itachi, Kisame intercepted Sasuke's team, Hebi, allowing only Sasuke to progress, and fighting with his old friend Suigetsu Hozuki to pass the time. Later, the fight was stopped by Suigetsu, who also informed them of Sasuke's victory over Itachi. Some time later, Kisame was confronted by Tobi, Deidara's partner, who revealed his true identy as the man Kisame believed to be Madara Uchiha that had controlled the Fourth Mizukage, Yagura. Later, after Sasuke and his team, renamed Taka, had seemingly captured the Eight-Tails, Gyuki's jinchuriki, Killer B, Kisame helped to begin the sealing but, after it was revealed to have been a fake, Kisame commented that b had fooled Sasuke. In the manga, the Six-Tails jinchuriki, Utakata, had already been captured and sealed before part 2, but in the anime, a filler arc focused on the Six-Tails and, after Pain, Akatsuki's public leader, captured Utakata, Kisame helped to seal the Six-Tails, before being given a new assignment.
As Sasuke had failed to do so, Obito(the fake Madara's real name) ordered Kisame to find and capture Killer B himself. After finding B, Kisame, after outdoing B's comrades, began to battle B in a fierce fight, with B not being able to fight at full strength due to the presence of his friends. B used his version 2 form of his Eight-Tails cloak to blast away Kisame's rib area, forcing him to fuse with Samehada, his living sword, to heal. As this also allowed Kisame an even more shark-like appearence and greatly increase his power, he used his Water Release: Great Exploding Water Colliding Wave technique to create a giantdome of water capable of moving in conjunction with Kisame, who was much faster in the water. Though B managed to counter somewhat by partially transforming into the Eight-Tails, Gyuki, growing a couple of tentacles and grabbing Kisame. Though B managed to drag Kisame away and free his friends, impressing him, Kisame managed to continue absorbing B chakra as he had been doing all during the fight and he beat B unconscious. Dispelling the dome, Kisame attempted to cut off B's leg, but was betrayed by Samehada, which had grown fond of B's chakra and gave him some of Kisame's. Kisame then tried to use one of B's swords for the same purpose, the latter threw a lightning-infused pencil at him and cut his cheek. Soon after, A, B's brother, arrived and after Samehada restored B's chakra reserves, the two worked together to behead Kisame with their Double Lariat move. However, Kisame had switched with a clone of his friend, White Zetsu, earlier in the dome and taken refuge inside Samehada, which B took possession of after the fight.
Kisame went on the gather information regarding the Allied shinobi Forces in the Fourth Shinobi World War. However, after Naruto Uzumaki mastered the Nine-Tails, Kurama's chakra, Kisame's presence was exposed and he was forced to flee. He once again encountered Might Guy, who once againcould not remember his name, which had annoyed him last time they fought. Though Samehada returned to B, Kisame was able to steal a lot of chakra from them both and regain his stronger body which had become weakened. Kisame then fought an even battle with Might Guy, who used seven of the inner Eight Gates and his Daytime Tiger move to defeat him. Though Kisame was restrained by Yamato's Wood Release, he managed to awaken himself by biting his tongue to prevent the Konoha and Mumogakure shinobi present from gaining any information on Obito or Akatsuki. He then, using pure brute strength, broke free from his restraints and, realizing escape was not possible, trapped himself with his Water Prison Technique, then summoning three sharks and allowing them to devour him. Shocked at the notion of his death, his enemies tried read the scroll he had made of the information he gather, but failed to send, only to find it booby trapped; everyone present was trapped in a respective Water Prison Technique with a shark, while another took the and made its way to Zetsu, giving away the alliance's moves with the jinchuriki and later forcing them to rely on the aide of Naruto new sensing ability to get an edge of the White Zetsu Army on Akatsuki's side.
Kisame was a staunch battle-lover, who never passed up an opportunity to fight and who would not hesitate to mutilate someone if he saw a reason and opening. He was, however, a loyal friend and comrade, always thinking of his good friend and partner, Itachi Uchiha's well being. He was one of the few Akatsuki members that got along well with his partner and was always very loyal to Itachi, always following his orders willingly and never acting to start a fight with others unless Itachi said or gave permission(this, however, had its downside, as Itachi would also force Kisame to end his fights unfinished if he saw a reason, which annoyed Kisame). Kisame thought of Itachi as such a good friend, that he even thought of him in his final moments before commiting suicide. He was also very loyal to Akatsuki, always siding with them no matter what and in the end, he gave his life in defense of their goals. Kisame was very proud of his power, but never arrogant and he, just like Itachi, never underestimated his opponents, shown in his open acknowledgement that he could not defeat Jiraiya, but stated forwardly that Itachi could fight toe-to-toe with him, showing his confidence in his partner and respect for his power.
As an S-rank Missing-nin and one of Akatsuki's strongest members, Kisame was an immensely powerful and dangerously skilled shinobi, in some ways the strongest member of Akatsuki. Kisame claimed to be the best in the Akatsuki in taking prey alive, as he could leave them on the brink of death without killing them for maximum incapacitation. In his frequent fights with Might Guy, one of Konohagakure's strongest shinobi, Kisame was able to fight him on even terms every time and proved to be more than a match for him. He was strong to force Guy to use six of the inner Eight Gates and the Morning Peacock technique when battling with a clone that had 30% of his power( in thsi fight, he also outmatched Guy's team of Chunin effortlessly) and strong enough to force Guy to use seven of them and the Daytime Tiger technique when fighting him personally. He was able to single-handedly defeat and capture Roshi, the Four-Tails, Son Goku's jinchuriki, despite the latter's great power of Lava Release, and merely complained of feeling a little tired after the battle, despite noting how hard it was to overcome Roshi. In his fight with Killer B, the Eight-Tails, Gyuki's jinchuriki, Kisame was able to overwhelm him without much trouble and nearly defeat him, though fairly this was only because the latter couldn't go all out and fight at his full power because of his comrades presence, and B would have easily defeated Kisame one-on-one. Kisame showed a good intellect, able to deduce the workings of Killer B's initial atatcks without any trouble and at a moments notice. He was also able to set a clever booby trap with his information scroll that caught many Jonin-level shinobi off-guard and trapped them in a Water Prison Technique, each with a shark and allowed one to get away with his scroll.
Kisame was a very powerful swordsman, able to easily kill his former master and use the latter's Samehada with great skill. Put together with Kisame's incredible physical prowess, he was very deadly in direct, close combat, able to easily overpower Asuma Sarutobi, a skilled Jonin of Konohagakure, while using his sword with one hand and bearing down with only the edge of the blade and outmatch the highly skilled Suigetsu Hozuki. He was also able to break free from Yamato's Wood Release restraints that were deadening his chakra with just his pure brute strength. When Killer B, the most skilled swordmen in the series, was at a lack of seven swords, Kisame was able to effortlessly outmatch his two swordplay. Kisame was a master of Water Release nature transformation, easily second only to the likes of Tobirama Senju, and had various, very powerful techniques at use that even Jonin found hard to fight against or at least a challenge. Suiting his shark theme, Kisame could create one of more sharks from water, which if used on a high enough scale, he was able to use to overwhelm Might Guy's Morning Peacock technique. despite its remarkable power and speed. He could also cause the water sharks to explode with great power. He could also summon up enough water at once to create a giant lake and a giant dome to entrap his opponents which could move with Kisame. When this technique was used in conjunction with Kisame's ability to fuse with Samehada, which granted him an even more shark-like appearence and the ability to breath under to water, Kisame could easily turn the tables on an enemy in overwhelming odds. Kisame had the most chakra of any of the Akatsuki, to the point that a clone of him with 30% of his chakra had as much as Naruto Uzumaki, and his mastery of tremendous water techniques further exampled his chakra prowess.