Goku in his Super Saiyan form.

As a member of the Saiyan race, Goku has acquired the ability to transform by physical training. By transforming his body, Goku greatly enhances his abilities from the previous state. Goku is also the only Saiyan in the entire series to achieve all known Saiyan transformations. As a child, he was able to transform into the Saiyan were-monkey called Oozaru. However, he was not able to transform into the Oozaru at will via a required component of special radiant waves emitted by a full moon. As with the Saiyan, Goku was born with a tail which is a vital characteristic for transforming into an Oozaru. It is removed later in the original Dragon Ball series, however, is regrown in the third sub-series Dragon Ball GT , helping Goku to transform into a Golden Oozaru. In the series, Goku is the first Saiyan to achieve the legendary transformation of Super Saiyan in over a millennium . Goku achieved this transformation when he was overcome by rage from the murder of Kuririn by the hand of Freeza. He continues to train this form throughout the series, eventually gaining two advanced states of the regular Super Saiyan called the Super Saiyan 2nd Grade and Super Saiyan 3rd Grade. Eventually, he masters every aspect of the Super Saiyan in order to challenge Cell. Goku then transforms even further to Super Saiyan 2 which was first seen in the fight against Majin Vegeta, but had been achieved during his training in Other World. Super Saiyan 3 was also obtained during his training in the Other World, first appearing in his fight with Majin Buu. During the sequel series Dragon Ball GT, Goku achieves his last transformation called Super Saiyan 4.