According to Wiki http://en.wikipedia.org/wiki/Shukongoshin
* "The origin of the image of Vajrapani should be explained. This deity is the protector and guide of the Buddha Sakyamuni. His image was modeled after that of Hercules. (...) The Gandharan Vajrapani was transformed in Central Asia and China and afterwards transmitted to Japan, where it exerted stylistic influences on the wrestler-like statues of the Guardian Deities (Nio)." (Katsumi Tanabe, "Alexander the Great, East-West cultural contacts from Greece to Japan", p23)