Tailed Beasts

The Tailed Beasts are the powerful concentrations of Chakra that take the form of powerful monsters that roam the lands throughout history. Occasionally, they have been sealed into the bodies of human beings known as Jinchuriki. With their powers and the abilities of their mortal hosts combined, together the Tailed Beasts and Jinchuriki become the most least important plot devices in anime history.

Fun Fact: Did you know that out of nine of the Tailed Beasts shown in this image, roughly two and a half are actually significant to Shippuden in any way?