Son Gokū

The is a tailed beast sealed within Rōshi of Iwagakure. Little is known about the Four-Tails, only that it allowed Rōshi to use its Lava Release abilities, a combination of fire and earth the likes of which have rarely been seen outside kekkei genkai. Kisame Hoshigaki of Akatsuki had difficulty capturing Rōshi because of this. The Four-Tails was later extracted and sealed, leading to Rōshi's death.

Conception
The design of the Four-Tails is a combination of a gorilla and the Ōzaru from Dragon Ball, and the master of Goku, the main character of said series, was also named Roshi. The horns on its forehead are modelled after the diadem worn by Sun Wukong from the classic Chinese novel Journey to the West.