Kisame Hoshigaki

Kisame Hoshigaki (干柿鬼鮫, Hoshigaki Kisame), feared as the Monster of the Hidden Mist (霧隠れの怪人, Kirigakure no Kaijin), was an S-rank missing-nin from Kirigakure's Seven Ninja Swordsmen of the Mist and was partnered with Itachi Uchiha when the latter joined Akatsuki. 

Source: http://naruto.wikia.com/wiki/Kisame_Hoshigaki

Background

Kisame while guarding the Cypher Division-nin.

Originally, Kisame was to guard the Cypher Division under orders from his superior, Fuguki Suikazan of Seven Ninja Swordsmen of the Mist. When the group was cornered by Konoha-nin under Ibiki Morino during a mission, Kisame chose to kill the Cypher Division members to keep their intel from being leaked out through Ibiki's interrogation, as instructed by Fuguki.

Kisame kills Fuguki and takes Samehada.

Eventually, learning that Fuguki was selling information to other ninja villages, Kisame killed him and took Samehada for himself while replacing his superior as one of the Seven Swordsmen. Since then, Kisame was given the title of "Monster of the Hidden Mist", and formed a connection with Suigetsu Hōzuki and Mangetsu Hōzuki.
While approached by the Fourth Mizukage Yagura to be commended him for his loyalty to Kirigakure, the ordeal from killing his fellow Kiri ninja to reach his status as a Mist Swordsman caused Kisame to become disillusioned and see himself as living a lie. It was soon after that Kisame met a mysterious ninja who was manipulating Yagura from the shadows and called himself Madara Uchiha. Learning of the Eye of the Moon Plan, Kisame was at first sceptical of the mysterious ninja but the notion of a "world of truth" enticed him to become one of the first and most loyal members of the Akatsuki.
Eventually, Kisame became a missing-nin when the Land of Water sought him for plotting to overthrow its government and being involved in numerous assassinations that include another country's daimyō. As a full-time member of Akatsuki, Kisame was partnered with Itachi Uchiha. Though they initially greeted each other with hostility, they became good partners.

Personality

Kisame slaughters his team-mates in order to protect important codes.

Kisame loves to fight and would not hesitate to mutilate his opponents, as seen when he suggested cutting off Naruto's legs to make him easier to carry, to prevent the latter from escaping on foot. Despite his aggressive nature, Kisame is very perceptive in battle, able to deduce the basics behind an opponent's technique and react to any potential danger he is aware of. However, being paired with Itachi, Kisame is usually unable to finish his battles with Itachi around, and he would inform his opponents that they "don't know how lucky they are". Kisame also has a deep loathing for Might Guy since their first encounter, with Guy's inability to remember Kisame prior to his death agitating him.
Originally when first partnered, Kisame warned an equally hostile Itachi to be careful of him. But in time, Kisame became one of the few members of Akatsuki that got along well with his partner despite the fact they had opposite personalities. The only common ground between both ninja being that they betrayed those close to them, Kisame is loyal to Itachi as he would only not take action unless ordered or after being given permission, but express concern for his friend's well being. Despite his pride, Kisame acknowledges Itachi as the stronger of the duo, evident by Kisame saying to Itachi that he himself couldn't defeat Jiraiya, but stated his certainty that Itachi could go one-on-one with the Sannin. In the anime, Kisame appeared saddened upon hearing of Itachi's death. Kisame ultimately considered Itachi as a good friend, even thinking of him in his last moments.
Other than believing everything he knew was a lie and desiring to see Tobi's "world of truth", Kisame lived strictly to protect valuable information as reflected in killing the Cypher Division to keep their intel from Konoha and executing Fuguki for selling their village's secrets; on a related note, he refused to bond with his team-mates when they were on a mission together. This ideal became his philosophy, ultimately motivating his assisted suicide when left with no other choice.

Appearance

Kisame's full appearance.

Kisame was a very tall and muscular shinobi, and was the tallest member in Akatsuki. He had a distinctive shark-like appearance, complete with pale, green skin, depicted as blue-grey in the anime, small, round, white eyes, gill-like facial markings under his eyes, and actual gills on his shoulders, and sharp triangular teeth, much like the other members of the Seven Swordsmen of the Mist. He also styled his blue hair in the form of a shark fin. As a member of Akatsuki, he also wore dark-purple nail polish. During his time as a Kirigakure shinobi, he sported the standard outfit of the village, complete with a flak jacket and a forehead protector. Later, he donned what appears to be the standard attire of the Seven Swordsmen which consists of: a dark sleeveless shirt paired with matching pants, provided with a waist guard, and striped arm and leg-warmers typical of his village. He also switched to a modified version of Kirigakure's forehead protector, which covered his ears as well. He kept this very same attire, under his Akatsuki cloak, even after defecting from the village, with the only differences being his leg-warmers, which were substituted by the organisation's standard ones; though later on, he also removed the shirt from its attire, remaining bare-chested. He wore his Akatsuki ring on his left ring finger, bearing the kanji for "south" (南, nan) which was yellow in colour.

Abilities

Kisame was a very powerful and dangerous S-rank missing-nin, whose strength earned him admittance into the Akatsuki. As a former member of the Seven Ninja Swordsmen of the Mist, Kisame is one of the most powerful shinobi ever produced within Kirigakure; in fact, he was able to easily kill his former master, who was a member of the Seven Swordsmen generation said to be the strongest in the history of the village, despite Samehada being in the opponent's hands at the time. He also successfully captured the Four-Tails' jinchūriki Rōshi by himself, despite noting his target's exceptional powers. Though a difficult task, by his own admission, Kisame merely complained that he was "a bit tired". He also claimed that he was the best in the Akatsuki at capturing targets alive as seen when he was able to capture Rōshi alive leaving him only "on the brink of death". During battles with Might Guy — one of Konoha's top shinobi — Kisame proved to be more than a match for him. He was even able to force Guy to open six of the Eight Gates while he was only at 30% chakra, and seven gates against the real Kisame.
Kisame also showed a keen intellect in battle, an example of which is deducing the nature of Killer B's attacks and tactics behind them during their first encounter.