Tailed Beast

In the Naruto universe there are at least nine "great" demons,called the tailed beasts. The Nine tailed fox demon is sealed inside Naruto. Gaara of the Desert used to have the one tailed demon sealed in himself. An evil organization, the Akatsuki, has an evil plan based on the capture of the tailed beasts.

History
It seems that the Demons (also referred to as bijuu) were around before the First Great Ninja War. The shinobi nations first involved these demons by attempting to capture them and harnessing their powers to defeat their enemies. It never worked out. A technique that is used to seal demons and use their power became available (description stated above), and the demons slowly became victims of this technique. Eventually, at the time period of the Naruto plot, very few demons roamed free in the world.

Jinchuriki
The term jinchuriki is first used by the Akatsuki to mean the shinobi that have a demon sealed within him or her. Naruto considers this term profane and derogatory. When a newborn baby has a demon sealed inside his or her body, the person develops signs of containing the bijuu. For example: Naruto has larger than normal canine teeth and stripes on his cheeks since his sealed demon is the Fox Demon. Gaara has dark lines outlining his eyes and his gourd resembles the pack that a tanooki carries around.

One Tailed Raccoon Demon

 * Name: Ichibi no Shukaku


 * Host: Gaara (former)


 * Appearance: Resembles a raccoon (or tanooki) that is made of sand


 * Abilities: Controls sand. Spits wind full of chakra

Two Tailed Demon

 * Name: Nibi no Nekomata


 * Host: Yugito


 * Appearance: Cat with two tails.


 * Notes: Abilities unknown, possibly linked to fire element

Three Tailed Demon

 * Name: Sanbi no Isonade


 * Host: None


 * Appearance: A fish-like creature

Note: Could possibly be in the form of a giant squid with 3 tentacles. Unconfirmed. Abilities unknown, possibly linked to water element

Four Tailed Demon

 * Name: Yonbi no Sokou


 * Host: Unknown Old Man


 * Appearance: A reptile-like creature


 * Note: Abilities Unknown

Five Tailed Demon

 * Name: Gobi no Houkou


 * Host: Unknown


 * Appearance: A dog-like creature


 * Note: Abilities Unknown, possibly linked to all 5 elements

Six Tailed Demon

 * Name: Rokubi no Raijuu


 * Host: Unknown


 * Appearance: Weasel-like creature


 * Note: Abilities Unknown, possibly linked to lightning element

Seven Tailed Demon

 * Name: Shichibi no Kaku


 * Host: Unknown


 * Appearance: Badger-like creature


 * Note: Abilities Unknown, possibly linked to illusions

Eight Tailed Demon

 * Name: Hachibi no Hachimata


 * Host: Unknown


 * Appearance: Snake-like creature


 * Note: Killed in Japanese mythology. Current existence unknown. Abilities unknown

Nine Tailed Fox Demon

 * Name: Kyuubi no Yoko


 * Host: Naruto


 * Appearance: A red fox with nine tails


 * Abilities: Nearly unlimited chakra, incredible strength, near instant healing rate.


 * Note: By far the most powerful bijuu. According to Japanese myth, its power is so great that it is unmeasurable. No bijuu has managed to defeat the Kyuubi in combat, even when allied against it.