Super Saiyan 4

Super Saiyan 4(超サイヤ人フォー, Supa Saiya-Jin Foa) is the final and most powerful stage of basic super saiyan transformation that can be achieved by those who carry the blood of saiyans. It is a transformation that was first reached by Goku during a titanic bout against majin buu, though the form was theorized to have existed thanks to son gohan, and the knowledge of the kai's who were aware of the existence of the transformation, thus allowing goku to assume it in response to the threat of majin buu. Since then, the transformation has been achieved by a number of other characters in the series.