One Tailed Shukaku
Names: One-Tailed Shukaku or Shukaku of the Sand, English TV "Shukaku the Sand Spirit/Demon"
Creature type: Tanuki (raccoon-dog, native only to Japan and other Asian countries)
Host: None, formerly Gaara.
Unique traits: Able to spit concentrated balls of wind mixed with chakra.
Status: Captured, extracted, and sealed by Akatsuki.
Shukaku is said to be the corrupted spirit of a Sand monk turned demon. He was originally sealed inside a teakettle and then placed inside his first host. He was sealed inside Gaara by Chiyo on the orders of Gaara's father, the Fourth Kazekage, using Gaara's mother as the sacrifice. Shukaku had two other hosts before Gaara, both of whom died when Shukaku was extracted from them. Shukaku is intelligent but also incoherent, giving him the demeanor of a drunkard, this fits well with the typical depictions of tanuki in Japanese folklore. Shukaku itself can translate to "drunk" in Japanese. Like other tailed beasts, its innate rage and bloodlust influence its behavior, and it relishes in the opportunity to kill anyone in sight.
As a host of Shukaku, Gaara has the ability to move and levitate sand at will, and is protected at all times by the Shield of Sand, regardless of his will (even self-inflicted injuries are prevented by the sand). He also suffers from lifelong insomnia, a side effect of being Shukaku's host. Should he fall asleep, Shukaku would eat away his personality.
When angry or particularly bloodthirsty, Gaara begins to transform into a human-sized version of the Shukaku by layering sand over his body. The sand takes on the appearance of the Shukaku, and enhances his abilities greatly. While in this form, Gaara gains immense strength, endurance, and the ability to use Sand Shuriken. The weak point of this transformation is at the base of its tail, where any strong enough blow (such as an exploding note) will cause severe damage to it. He can also stretch his sand limbs as he does with his regular sand, the primary difference being that his limbs remain just as strong as when they are retracted. This transformation seems to occur very slowly, as Gaara attempted to assume this form twice and was foiled both times. In the first instance, Sasuke injured him during an attempted transformation in the Chunin exam. The latter, which Gaara nearly completes, is ruined by Naruto during their battle in the forest. Gaara has only been able to reach a point at which all but his legs have been covered in sand.
In dire situations, Gaara can create a life-sized replica of Shukaku from sand. Unlike his human-sized version, this replica can be created almost instantly. Gaara controls the replica from within, remaining safe from enemy attacks. Despite being made of sand, Gaara seems to be unable to regenerate any damage caused to the replica. While in this form, Gaara can also release Shukaku's spirit, allowing the demon to use his full power. To do this, Gaara must emerge from within the replica, settling on the top of its head, and force sleep upon himself. Once released, Shukaku can attack with his signature ability, Wind Release: Drilling Air Bullet. Because Gaara protrudes from the top of Shukaku's head, he can be awoken, thus suppressing Shukaku's spirit once more.
During the Rescue Gaara arc, Shukaku was forcefully extracted from Gaara by Akatsuki, thus killing him. Fortunately for Gaara, he was resurrected through a combination of Chiyo's life-transferring technique and Naruto's chakra. Gaara's ability to control sand still appears to be intact, though to what degree remains unclear.