Hera, who has hated Heracles since before his birth as the son of Zeus and a mortal woman, afflicts him with a fit of madness in which he kills his own wife and children, believing them to be enemies. Seeking purification for the killing, Heracles consults the oracle at Delphi, which tells him to serve his cousin, the weak and jealous King Eurystheus of Tiryns and Mycenae, for twelve years, performing whatever labors Eurystheus assigns.
The early labors pit Heracles against monstrous animals threatening the Argolid and beyond: strangling the invulnerable Nemean Lion with his bare hands after his weapons prove useless against its hide, then wearing the lion's own skin as armor afterward; beheading the many-headed Lernaean Hydra with his nephew Iolaus's help, since each severed head grows back two more unless the wound is cauterized immediately; capturing alive the Golden Hind of Artemis and the ferocious Erymanthian Boar without permanently harming either; and cleaning the vast, filthy stables of King Augeas in a single day by diverting two rivers through them, a labor Eurystheus later tries to disqualify on the grounds that Heracles was paid for it.
Eurystheus, unnerved by the ease and speed with which Heracles was completing tasks meant to kill him, is said to have taken to hiding inside a large storage jar whenever Heracles returned to report a labor finished, communicating with him only through a herald rather than face him directly, an image later Greek vase painters returned to repeatedly as a way of contrasting the hero's fearlessness with the king's cowardice.