Tailed Beast

In the Naruto universe, there are nine giant demons called the that inhabit the planet. They are actually living chakra in physical form, often referred to as "Chakra Monsters". The Akatsuki organization has a plan that involves the capture of the Tailed Beasts.

History
The Tailed Beasts are Retarded

Legend of the Tailed Beasts
According to some fans, the "Legend of the Tailed Beasts" is an epic story from Japanese folklore which Naruto author Masashi Kishimoto draws from to create the Tailed Beasts in his work. However, it is an example of internet-based fakelore which originated on Chinese websites, some suspect this chinese site.

The veracity of the legend breaks when it is cross-referenced with non-fandom sources on Japanese folklore. For example, the isonade, which is held to be the Three-Tails in this account, is in fact equipped with only one large, hook-covered tail, and the "houkou" which is actually a Chinese creature called penghou, named as the Five-Tails, has no tail at all. The badger was said to be the lord of all these beasts in the original legend, and Naruto fans have claimed certain Bijū to be a badger instead of it's true form which was a tanuki for Ichibi no Shukaku and a bat for Shichibi no Makumore)

Additionally the author of the story admitted it was not a true legend, unfortunately it has gone largely unnoticed by most fans of the story.