Prof. Meir Shahar's book The Shaolin Monastery mentions how Vajrapani, the protector of the Buddha, was worshiped as the de facto guardian deity of the Shaolin Monastery. One legend set during the Red Turban Rebellion in the Yuan Dynasty states the rebells were besieging the monastery when a lowly kitchen worker threw himself into an oven and emerged a mountain-striding giant wielding a long fire poker as a makeshift staff. After he had defeated the rebells, all of the other monks realized that it was none other than Narayana (one of the his Chinese names). Thus, he was also worshiped as the progenitor of the famous Shaolin staff method.
A Shaolin stele portraying Vajrapani in his Narayana form
Another legend says that devotees could gain supernatural strength and boxing abilities if they prayed to him most ardently. However, this strength could only be achieved by him 'force-feeding' the vegetarian monk raw meat. This legend is the root of all “meat-eating martial monks”. (It's important to note that Bodhidharma was not associated with Shaolin arts until 1629, when the Sinew Changing Classic was written by a Taoist.)
Prior to and slightly after entering China, the Buddhist version of Vajrapani was always depicted with a club instead of a staff. His name actually translates as "thunderbolt in hand". According to several books, his portrayal as a muscular, club-wielding man was supposedly influenced by statues of the Greek hero Hercules.
Tang Dynasty depiction of Vajrapani
Greek statue of Hercules
A Greco-Buddhist culture thrived in Pakistan, Afghanistan, and India during the 4th century BCE to the 5th century CE. In fact, the 2nd century ruler Menander I was the first recorded westerner to convert to Buddhism. These people were known for their Greek influenced art.
Greco-Buddhist statue of Vajrapani (left) and Buddhist monks
Greco-Buddhist statue of the Buddha and Vajrapani (right).
Did you notice how in all the statues of Vajra and Herc, besides the club and bare chest, one of the central motifs seemed to be him shifting his weight onto one leg? Look at them again.
If statues of Hercules truthfully influenced Vajra's look, then Herc indirectly influenced Shaolin lore. Another interesting thing is that the Spartans believed themselves to be descendants of Hercules. So, the Greco-Buddhist art has a connection to both the Spartans and Shaolin warrior monks. How cool is that?