The Labors of Hercules are a series of episodes concerning a penance carried out by Heracles, the greatest of the Greek heroes, whose name was later romanized as Hercules. They were accomplished at the service of King Eurystheus. The episodes were later connected by a continuous narrative. The establishment of a fixed cycle of twelve labors was attributed by the Greeks to an epic poem, now lost, written by Peisander, dated about 600 BC.

Source: Wikipedia