In the Naruto World, there exists nine very powerful Biju, or tailed demons. Each Biju is characterized with the number of tails it possesses and are named according to this. All are very powerful and have an unprecedented amount of chakra. These tailed demons are scattered all over the world. During the Great Ninja World, countries try to capture the tailed demons and use them as weapon. Their power are far beyond human understanding, they cannot be control. Those who have a Bijuu sealed within them are known as Jinchuriki, meaning "power of human sacrifice". Bijuu gain  unimaginable power when they are join with a Jinchuuriki. A Jinchuuriki that get their Bijuu extracted from their body dies.

Ichibi - 1 Tail Shukaku

Shukaku Jinchuriki: Gaara
Relation: Wind Country
Shukaku is known as one of the tailed beasts in the Naruto world. Shukaku was sealed into Gaara by his father, Kazekage Fourth. Shukaku has been the reason that the sand is protecting Gaara. During the invasion of Konoha, Gaara turns into the final form of the Shukaku, nearly destroying the village. But Naruto was able to summon Gamabunta who helped Naruto smack Gaara awake and put an end to the Shukaku's rampage. Gaara is the third shinobi in Sand Village to inherit the Shukaku.

Kyuubi - 9 Tails Demon Fox

9 Tails Demon Fox Jinchuriki: Naruto Uzumaki
Relation: Fire Country
The 9 Tails Demon Fox is one of the legendary tailed demons. With the single swipe, his tails would flatten mountains and cause tsunamis. When the 9 Tailed Demon Fox attacked the Leaf Village, Hokage Fourth gave up his life and sealed it away in a newborn baby name Uzumaki Naruto. Now within the body of Naruto, the 9 Tailed Demon Fox powers are part now part of Naruto. Before he was able to control the chakra of the 9 Tailed Demon Fox, the 9 Tailed Demon Fox powers were often let out by rage and anger. During the training with Jiraiya, he was taught how to control is ability to use the chakra of the 9 Tailed Demon Fox. Often, the 9 Tailed Demon Fox lends its powers to Naruto to save his life and Naruto's life. Due to the 9 Tails Demon Fox power, Akatsuki is now after it.