Shukaku

, more commonly known as the, is a tailed beast that was last sealed within Gaara of Sunagakure after being sealed in two other hosts. It has been captured by Deidara, then extracted and sealed by Akatsuki.

Background
Shukaku first came into being in the waning days of the Sage of the Six Paths, who used his Creation of All Things ability to separate the Ten-Tails' chakra from its body and divide it into nine separate constructs that would come to be known as tailed beasts in order to ensure that it would never resurface after his death. Some time after being created, the Sage sat down with all the young tailed beasts and told them that they would always be together, even when separated, and that one day they would become one entity again with different names and forms than they did. Then, when the time came, they would know what true power is.

Shukaku would eventually be captured and kept by Sunagakure. The citizens of Sunagakure came to believe that Shukaku was a of a corrupted Suna priest originally sealed inside a tea kettle. When Hashirama Senju called the first five Kage into the first summit, the First Kazekage attempted to use their possession of Shukaku as leverage to gain wealth for his nation, as opposed to gaining another tailed beast.

Shukaku had two previous jinchūriki, one of which inspired the Third Kazekage to create the Iron Sand technique. Shukaku was eventually removed from their bodies, resulting in their deaths.

When Karura became pregnant with Gaara, her husband, the Fourth Kazekage, had Chiyo seal Shukaku into Gaara while he was still in the womb, because, out of his three children, Gaara was the only one compatible with the tailed beast. Before Karura died after giving birth, she passionately told her son that she would protect him, and, according to her husband, her love seeped into the sand and was noted to form his automatic defence. However, Gaara couldn't properly control Shukaku's powers, killing or injuring several of Suna's shinobi and citizens by accident. Deemed a failure, the Fourth Kazekage chose to test his son one last time, ordering Yashamaru to assassinate him and also tell him that his mother never loved him, and that she was used as a human sacrifice for the sealing process. Gaara failed the test, fully releasing the rampaging Shukaku, to which the Fourth eventually used his Gold Dust to subdue the tanuki.

Personality
Shukaku is cunning, but also incoherent, giving it the demeanour of a madman. According to Gaara, because of its innate rage and blood-lust, Shukaku relishes the opportunity to kill anyone in sight, even more so during a full moon. Like all tailed beasts, Shukaku has a strong desire to preserve its own life, and as such, will grant its jinchūriki the power to control sand as well as allow them to transform into it in a state of need and blood-lust. Gyūki mentioned that Shukaku hates Kurama for its beliefs that the tailed beasts' strength is measured by the number of tails and, as such, views Shukaku as the weakest.

Appearance
Shukaku is a sandy-brown coloured tanuki, with black (dark blue in the anime) markings all over its face, body, and tail. It has a jagged, concave mouth and the sclerae of its eyes are black, with yellow irides and pupils that each takes the shape of a black four-pointed star with four black dots around it. During the last days of the Sage of the Six Paths, Shukaku in its youth looked the basically same as it does presently, only much smaller.

Abilities
As a tailed beast, Shukaku possesses a large quantity of chakra and can perform the Tailed Beast Ball. The tanuki's most notable ability is its sand manipulation, using it as an effective weapon. Since its whole body is completely made of sand, Shukaku can ignore most damage that would otherwise be detrimental, as shown when it had one of its arms chopped off by Gamabunta and was still able to keep on fighting. In addition, Shukaku is able to use Wind Release nature transformation, which it uses to perform powerful attacks such as the Wind Release: Drilling Air Bullet that can create giant craters upon impact. It is shown that whenever Shukaku is sealed into its jinchūriki, it has the ability to eat away its host's personality, and influence him or her with its bloodlust behaviour whenever they sleep, which leads its host to develop insomnia.

Invasion of Konoha Arc
During the Invasion of Konoha, Gaara transformed into his full Shukaku form during his fight with Naruto Uzumaki, who later summoned Gamabunta. When Gaara exposed himself on top of Shukaku's head and used the Feigning Sleep Technique, Shukaku took full control of its body and battled them. Shukaku's power was too much for Gamabunta to handle, resulting in both him and Naruto using the Combination Transformation to take the form of a giant fox (Kurama in the anime). Gamabunta used the form's claws and teeth to grab and restrain Shukaku, in order for Naruto to wake Gaara up with a punch, which suppressed Shukaku's power.

Kazekage Rescue Arc
During Gaara's time as the Fifth Kazekage, Deidara and Sasori from the Akatsuki were assigned to capture Shukaku. After Deidara defeated Gaara in combat and took him to Akatsuki's lair in the Land of Rivers, Shukaku was forcefully extracted from Gaara and placed within the Demonic Statue of the Outer Path. Though the extraction killed him, Gaara was resurrected through Chiyo's One's Own Life Reincarnation technique and has still retained the ability to control sand.

Video Games
Shukaku appears as a boss in Naruto: Ultimate Ninja Storm and Naruto: Rise of a Ninja, and a false replication of it is a boss in Naruto Shippūden: Kizuna Drive. Shukaku itself is playable as its full form in Naruto: Ultimate Ninja 3, and Gaara takes on its miniature form in Naruto: Ultimate Ninja 3, 4, and 5.

Trivia

 * literally means 'protector crane'.
 * A is a popular figure in Japanese folklore and is famous for its mischievous nature and abilities to shape-shift. Tanuki are also said be rivals to the kitsune, which created an old Japanese proverb:, meaning two sly characters trying to outsmart one another. Shukaku being sealed inside a tea kettle is a reference to one Japanese tale called Bunbuku Chagama. In addition, Shukaku being claimed to be a corrupted Suna priest earlier in the series, has ties to a legend in the Kenchō-ji temple of a tanuki disguised as the shrine's priest.
 * Shukaku is the first tailed beast to have its name revealed in the series. In addition, Shukaku is the only tailed beast that controls a physical property rather than a chakra-based element, and hasn't shown the characteristic red-chakra-shrouded Version 1 or Version 2 forms (this is presumable due to Shukaku appearing early in the story and Masashi Kishimoto having not defined the abilities of the tailed beasts or the fact that Shukaku and Kurama were related at all).
 * Shukaku is also the only tailed beast that has not been resealed into its former host during the Fourth Shinobi World War. However, when chapter 629 was first released, Shukaku's image was seen among the tailed beasts, despite not giving Naruto its chakra like the others, suggesting an error. Later in the tankōbon version, it's been removed.

Quotes

 * (To Naruto and Gamabunta) "I'm finally out!! And here's someone that I want to kill right now!!"