Kugaya

Kugaya (can also be written as Kuugaya) ois a mysterious and ancient ungodly beast of destruction. They say that he (it) attacked the Earth a long time ago because in his dark heart he wanted only destruction and thrived only of destruction. Kugaya's powers are mostly unknown, but some say that he could destroy entire worlds when in his prime, and the only reason he didn't do so to Earth was beacuse he was too arrogant and couldn't imagine the possibility of him getting defeated. And because of that arrogance, the Sage of the Six Paths and the Ronin of the Hidden Destiny managed to defeat him by splitting his chakra in it's Yin and Yang halves. The Yin half, which contained all his cunning and darkness, was sealed inside the Moon by the Sage's Chibaku Tensei. The Yang half, containing his raging destructiveness, was permantently combined with the soul of the Ronin of the Hidden Destiny. The location of the Ronin along with the Yang half of Kugaya's chakra is unknown by the moment.

It's unknown what the Tailed Beasts think of Kugaya or if they even know of his existence.