Son Gokū

The is a demon formerly sealed within Rōshi of Iwagakure.



Background
It is currently unknown of what type of animal is the Four-Tails. Rōshi was defeated by Kisame Hoshigaki right after his introduction. According to Kisame, he had a difficult battle because he had to face many elemental fusions.

The Four-Tails was later extracted and sealed, leading to the old man's death.

If the Japanese folklore Legend of the Tailed Beast is followed than the Four-Tailed Beast is most likely the snake/rooster hybrid known as Sakou. Sakou has the lower body of a snake and upper body of a rooster, strongly resembling the western mythilogical beast the cockatrice, though Sakou does not possess wings. Sakou moves about by slithering or crawling and is said to be able to control poisonous gas and various venoms. Sakou slumbers in Mount Fuji and it is said when he sleeps that his snoring causes the volcano to erupt.

Activity inside Rōshi
Little is known about the Four-Tails' abilities. As the Four-Tails' host, Rōshi has made use of its Lava Release techniques, which is rarely seen outside of kekkei genkai. The fact that Rōshi is able to use Lava Release techinques further indicates that the Four-Tailed beast is the legendary Sakou.