What is the origin of the idiom herculean task?

Hercules is a figure in classical mythology. He was given the "Twelve Labours," which required 12 difficult tasks: slay the Nemean Lion, slay the nineheaded lemaean Hydra, capture the Erymanthian Boar, Clean the Augean stables in one day, and on and on. Many statues and painting portray the labors. So a Herculean task is labor intensive.