The Tailed Beasts (尾獣, Bijū) are nine giant monsters that serve to drive the plot of the Naruto series. They are differentiated by the number of tails they have, ranging from one to nine. The tailed beasts are large, living forms of chakra, sometimes referred to as "Chakra Monsters" (チャクラのバケモノ, Chakura no Bakemono), giving them power that far outmatches most shinobi. However, this immense strength is tempered by their bestial nature, which restricts them from being intelligent enough to use it effectively. As such, when the tailed beasts are sealed within humans, they are able to benefit from the knowledge of their hosts, giving them the ability to better utilise their powers.
The jinchūriki (人柱力; Literally meaning "Power of Human Sacrifice") are humans that have tailed beasts sealed within them. They exhibit extraordinary powers, and in some cases are more powerful than their tailed beasts, because they have the intelligence to use the beasts' powers effectively.
Shukaku (守鶴, Shukaku), better known as the One-Tailed Shukaku (一尾の守鶴, Ichibi no Shukaku) is a tailed beast that was sealed within Gaara. It has been captured by Deidara, then extracted and sealed by Akatsuki.
The Two-Tails (ニ尾, Nibi), Matatabi, is a tailed beast sealed within Nii Yugito of Kumogakure. It has been captured by Hidan and Kakuzu, then extracted and sealed by Akatsuki. It was later resealed into a resurrected Yugito during the Fourth Shinobi World War.
The Three-Tails (三尾, Sanbi), Isobu, is a tailed beast that was formerly sealed in Yagura of Kirigakure. It has been captured by Deidara and Tobi, then sealed by Akatsuki. It was later resealed into a resurrected Yagura during the Fourth Shinobi World War.
Son Gokū (孫悟空, Son Gokū), better known as the Four-Tails (四尾, Yonbi) is a tailed beast sealed within Roushi of Iwagakure. It was captured byKisame Hoshigaki, then extracted and sealed by Akatsuki. Son was later resealed into a resurrected Rōshi during the Fourth Shinobi World War.
The Five-Tails (五尾, Gobi), Kokuou, is a tailed beast sealed within Han from Iwagakure. It has been captured, extracted, and sealed by Akatsuki. In the anime, the Five-Tails is indicated to have been one of the two tailed beasts that Akatsuki captured before the start of Part II. It was later resealed into a resurrected Han during the Fourth Shinobi World War.
The Six-Tails (六尾, Rokubi), Saiken, is a tailed beast sealed within Utakata of Kirigakure. It has been captured by Nagato in the anime, then extracted and sealed by Akatsuki. It was later resealed into a resurrected Utakata during the Fourth Shinobi World War.
The Seven-Tails (七尾, Nanabi), Choumei, is a tailed beast sealed within Fuu from Takigakure. It has been captured, extracted, and sealed by Akatsuki. In the anime, the Seven-Tails is indicated to have been one of the two tailed beasts that Akatsuki captured before the start of Part II. It was later resealed into a revived Fū during the Fourth Shinobi World War.
The Eight-Tails (八尾, Hachibi), Gyuuki, is a tailed beast sealed within Killer B of Kumogakure after his cousin, cousin's uncle, and cousin's father failed before him.
Kurama (九喇嘛, Kurama), better known as the Nine-Tailed Demon Fox (九尾の妖狐, Kyūbi no Yōko), is the tailed beast sealed within Uzumaki Naruto of Konohagakure and was previously sealed within Uzumaki Kushina and Uzumaki Mito before her.