Son Gokū Seiten Taisei (孫悟空斉天大聖), more commonly known as Son Gokū (孫悟空) or simply the Four-Tails (四尾, Yonbi), is one of the nine tailed beasts. It was last sealed within Rōshi of Iwagakure. After the fourth shinobi war, Son returned back to Suirendo.
Son Gokū is a red-furred and green-skinned monkey, with a body-build of a gorilla. It has eyes with yellow irides and white pupils, spike-like protrusions along the length of its tails, elongated blunt fangs, and two long horns curving upwards on its forehead like a crown (both its fangs and horns are dark-tipped). In its mouth, Son doesn't have a tongue, but has an opening that is shaped like a dome volcano. During the last remaining days of the Sage of Six Paths, Son was much smaller and leaner with smaller fangs.
Son Gokū is a very prideful tailed beast, as it detests being called by the name "Four-Tails" and boasts about its lineage. It uses "ore" (オレ) when referring to itself.
It also hated humans, due to the fact that humans had enslaved it, and believes that apes are more intelligent than humans. However, when talking about the Sage of Six Paths, it showed him great respect, being that also had, apparently, a very deep relationship with him, never forgetting his final words. It also seems to have taken a liking to Naruto Uzumaki, as it was moved by his actions for truly trying to save it from being controlled by Tobi and even gave him some of its chakra before being sealed away. He also treats his fellow tailed beasts with much respect, as he addresses them by their name, as seen with Kurama. Son also has a high amount of respect for those who respect the tailed beasts.