A (Fourth Raikage)

is the and the leader of Kumogakure. He is also the older brother of Killer Bee, the jinchūriki of the Eight-Tailed Giant Ox. It is hinted that Killer Bee, and therefore Killer A as well, comes from the Yotsuki clan. Knowing Yugito Nii's and Killer Bee's immense powers if they were to ever transform into their full demon forms, he forbade at least Killer Bee from doing so.

Appearance
Killer A has a lot of similarities with his younger brother. He is a tall dark-skinned man with a large muscular build, slicked-back white hair with a yellow tint, a few wrinkles, and a small moustache and beard. As of chapter 464, Killer A has lost his left forearm from just under the elbow; due to his left arm being burned by the inextinguishable black flames of Amaterasu inflicted by Sasuke during their bout, Killer A was forced to amputate it himself before it could spread further. Ironically, Killer Bee mentioned Killer A is left-handed.

Unlike other Kage, Killer A seems to wear his Kage cloak and hat on a regular basis, without a shirt underneath which further displays his hulky physique. He has black shuriken tattooed on both shoulders. On each wrist he has gold bangle bracelets, which seems to have protrusions that can jut out when he attacks, and has a gold belt on his waist with a lion's face engraved in the center. All of these aspects combined gives Killer A the appearance of a professional wrestler.

Personality
He is very caring and protective towards his younger brother, despite Killer Bee's status as a jinchūriki, and wept at the idea of his younger brother being captured by Akatsuki. However, when Killer Bee's ploy to use the affair to have a vacation was discovered, Killer A was furious, and swore to punish his little brother for it.

He is also headstrong and easily excited, smashing a desk apart when news of his brother being captured arrived. He also burst through a palace wall (probably from inside his own office too) to attend the Kage Summit. His assistant implied that this wasn't the first time. This suggests that he is quite destructive while in this mental state.

He also has a very stern and decisive personality, seemingly unaffected by Naruto's pleas for Sasuke's life. In his eyes, respect and strength mean everything in the ninja world. He believes that the weak should and will be crushed. This correlates with his philosophy that a ninja should never compromise or bow down in front of another ninja. Killer A has also been shown to be very suspicious of the other ninja villages, accusing all of them of working with Akatsuki and questioning their loyalties.

In battle, Killer A is shown to be physically brutal, as he uses extreme physical force to devastate his opponents, and is willing to sacrifice a limb, rather than lose a chance to defeat his opponents.

Invasion of Pain arc
Killer A is first seen enraged by news of Killer Bee's capture by Akatsuki. When he learns that the culprit was Sasuke Uchiha, a missing-nin from Konoha, he complained about why the Hokage had not dealt with him, compared to how fast they had dealt with the Hyūga Incident. With Killer Bee's capture coming so soon after that of Yugito, Killer A calls for a meeting of the five Kage to discuss Akatsuki. He also instructs Team Samui to inform Konoha that he will personally deal with Sasuke.

Five Kage Summit arc
Killer A departs for the Kage summit with two bodyguards: Darui and Shī. On their way to the Land of Iron they reunite with Team Samui, who provides them with information on Sasuke acquired in Konoha. Shi quickly discovers that Team Samui has been followed by Naruto Uzumaki. A keeps his men from attacking Naruto and agrees to listen to what he has to say. Naruto pleads for the Raikage to spare Sasuke, but his request is flatly refused and the Raikage berates him for sticking up for a criminal.

Once the Kage summit gets underway, Killer A quickly shows his disapproval of the other villages by smashing the table in front of him, prompting all of the bodyguards to come to theirs Kage's aid. After they return to their position, A points out that only Kumogakure has never had an Akatsuki representative, nor has it ever employed Akatsuki for a battle. He insinuates that the current Hokage, Danzō, used Akatsuki to dispose of the Third Hokage and the Fourth Kazekage. When Danzō is nominated for leading a joint taskforce to deal with Akatsuki, Killer A is outraged. Before he can raise much of an objection, however, Zetsu appears and tells those in attendance that Sasuke is nearby.

Killer A and his bodyguards immediately mobilize to go after Sasuke. They are drawn to Taka's battle with the Land of Iron's samurai, and after Shī tells him that the chakra are straight below them the Raikage bursts through the floor where they encounter Sasuke and his team. A easily destroys Suigetsu's sword and Jūgo transforms to the second stage of his Cursed Seal he starts a fight with him. Although Jūgo initially appears to have the advantage, A is able to punch a hole through his arms and into his chest and evade his attacks, before finally defeating him.

Sasuke and Killer A begin fighting. With his Lightning Release Armor, A avoids most of Sasuke's attacks, deflecting his lightning charged sword and is barely wounded by his Chidori. He delivers a series of physical attacks to Sasuke, but the final assault is negated as Sasuke uses an incomplete Susanoo to protect himself. Sasuke attacks with Amaterasu, which A dodges, and then coats his Susanoo with Amaterasu's flames to deter additional physical attacks. In his growing rage, A ignores this and attacks through the flames, causing his left arm to catch flame, but still smashes through the defense and hits Sasuke.

When A prepares another "final blow", Sasuke begins staging a counterattack. But the Kazekage, Gaara, intervenes using his sand to block another clash between the two. A is angered by the interruption, but Gaara states that continuing his attack would only cause additional injury. While Gaara speaks with Sasuke, A severs his arm and instructs Shi to stop the bleeding with his medical ninjutsu so that he can rejoin the battle. After Sasuke uses Susanoo to destroy the pillars and cause the ceiling to collapse, A uses his lightning-fast speed to crush the falling pieces of the ceiling. However, Sasuke used this as a diversion, to which A exclaims that he and the rest of his allies should chase him down. He later learns from Madara Uchiha that his brother is still alive, which both shocks and angers him. He realizes what Bee's plan actually was and says he'll punish him with his "Iron Claw".

After Madara reveals his "Moon's Eye" plan to take control of the world and declares the start of the Fourth Great War, he disappears. It is then brought up the need of an alliance between the Five Great Nations. Mifune nominates Killer A to be the leader due to how well he handled himself against the enemy already and because he could better control Killer Bee than anyone. After asking the other Kage, it was agreed to make him leader of the Shinobi Alliance.

Killer A's first decision was to locate his younger brother before he would fall into the hands of Akatsuki. He and his men managed to find Killer Bee in time fighting Kisame Hoshigaki, thanks to Kisame's reckless tactics. Together, the Raikage and his younger brother finished off Kisame with a Double Lariat.

Abilities
As the Raikage of Kumogakure and Leader of the Shinobi Alliance, Killer A is undoubtedly a powerful shinobi. His younger brother Killer Bee also mentioned in his fight with Sasuke that, before him, only Killer A was able to deflect the Eight-Tails. Karin notes that the Raikage's chakra level is comparable to that of a tailed beast.

Immense Physical Prowess
Killer A uses a 'power' types fighting style, he posesses a great deal of physical strength, as he first appeared lifting a large amount of weight with just one hand, and broke his desk with a single punch. His strength is further displayed at the Five-Kage summit when he punches through a wall, the floor, and even snapping Suigetsu's sword in two (albeit the sword already had a partial crack in it from Suigetsu's duel with Killer Bee). A was also able to punch a hole in Jūgo's arm and chest with ease, despite the latter being armored with his Level 2 Cursed Seal transformation.

Despite his large physique, the Raikage is noted for being very fast, grabbing Zetsu's throat before he had a chance to react. Befitting his appearance, the Raikage seems to prefer taijutsu combat to which he has shown tremendous prowess at. In addition to powerful punches, he is shown able to use equally impressive throws and take-downs. He prefers using wrestling techniques to more traditional forms of taijutsu.

He is shown to have an immense tolerance for pain, as he was able to withstand having his arm set on fire by Amaterasu and cutting it off without flinching.

Elemental techniques
On top of his physical capabilities, Killer A is also skilled in lightning-based jutsu, releasing a continuous surge of electricity from his body when confronting Sasuke. This electricity acts as a compliment to A's natural physical strength and speed to the point where he claims not even the Sharingan should be able to keep up with his movements. This is due to electricity stimulating his nervous system and speeding up his neural synapses, amplifying his reflexes. While using this ability, he is able to dodge Jūgo's multiple chakra blast and Amaterasu, both at point blank range. His speed in this state is greatly increased, to the point that it was mentioned by Shi that A's nervous system and reaction speed becomes comparable to that of the Fourth Hokage, Minato Namikaze.

The electricity can also work as a powerful defense. By momentarily increasing the electrical surge, Killer A was able to deflect a strike from Sasuke's Kusanagi Sword: Chidori Katana from behind and receive only a minor wound on his chest from a direct Chidori strike. With combining his lightning power with the full force of his chakra, just its sheer energy is strong enough to demolish all matter around him.

He has also shown the ability to use the focus lightning chakra into a sharp enough point to neatly cut through human limbs.

Trivia

 * His name is the Japanese pronounciation of the English letter "A". This is similar to the names of Killer Bee, Shī, and Jei, that are the pronounciations of the letters "B," "C," and "J," respectively.
 * A is known to be left-handed but he cut it off so now he is right-handed as a result.
 * Despite being left handed, A was fully willing to sacrifice it to injure Sasuke, most likely in attempt to hurt him as much as possible.