The 9 Tailed Beasts were created by Hagoromo Otsutsuki by using the Creation of All Things Technique to split the chakra of the 10 Tails. These Tailed Beasts are exceptionally strong, and have huge amounts of chakra. However, there are a few characters who can defeat them all at once.
5. Naruto Uzumaki
Naruto Uzumaki is the Jinchuuriki of the 9 Tails himself, and also has the chakra of all 9 Tailed Beasts. He also possesses Six Paths powers, along with Truth seeking orbs, which make him one of the strongest characters in Naruto. Without a doubt, Naruto can defeat all 9 Tailed Beasts at once, although there is no need for him to do so.