Bijuu are demons that exist in the world of Naruto, they are also known in as demons in Japanese mythology. There are nine in total. Each one has an incredible amount of chakra within them, to try and combat these powerful beasts and stop the destruction they cause they were captured and sealed inside new born babies using a powerful technique that would kill the person using it. The Fourth Hokage was one of those people who sacrificed their life to seal a Bijuu and protect the world from chaos. When the human has a demon sealed inside them they are known as Jinchuriki, so far there are only two known Jinchuriki and they are Gaara and Naruto. Every demon has a different amount of tails, ranging from one tail to nine.

Seal used on Naruto

One Tailed Demon - Ichibi no Shukaku, takes the form of a racoon. This demon is sealed within Gaara of the Desert, because of this Gaara has the ability to control the sand around him. Other translations include: Shukaku, One tailed Shukaku, Tanuki.

Two Tailed Demon - Nibi no Nekomata, takes the form of a cat in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Three Tailed Demon - Sanbi no Isonade, takes the form of a fish in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Four Tailed Demon - Yonbi no Sokou, takes the form of a reptile like creature in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Five Tailed Demon - Gobi no Houkou, takes the form of a dog in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Six Tailed Demon - Rokubi no Raijuu, takes the form of weasel in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Seven Tailed Demon - Shichibi no Kaku, takes the form of a badger in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Eight Tailed Demon - Hachibi no Hachimata, takes the form of a snake in Japanese mythology. This demon has not featured in the Naruto series as of yet.

Nine Tailed Demon - Kyuubi no Yoko, takes the form of a fox. This demon is sealed within Uzumaki Naruto who has incredible stamina and can summon large amounts of the Kyuubi's chakra. However Naruto has not yet learned how to fully control the awesome power of Kyuubi. Other translations include: Kyuubi, Nine Tailed Demon Fox, Kitsune.