Hercules, the son of Zeus and Alcmena, is an immortal god with the strength of a lion. He obtained immortality when he drank the milk of the goddess Hera, who threw him off for suckling too hard. Her spilled milk became the Milky Way. Though immortal, Hercules asked his father to let him die while he was suffering from a skin-burning poison.
After learning the Hercules was the result of her husband Zeus' affair with Alcmena, Hera retaliated by driving Hercules mad. In his crazed state, he ended up killing his wife and children. He sought advice from the Oracle of Delphi about how to ease his guilt, and she told him a list of labors he must complete in service to his cousin, King Eurystheus.
Depending on the story, Hercules performed 10 or 12 labors, including killing the multi-headed Hydra, conquering and returning with the Nemean lion, capturing the Cretan bull and stealing the Amazon Queen Hippolyta's girdle. Some stories also have him retrieving the golden apples of Hesperides and traveling into the Underworld to capture the three-headed dog Cerberus. Because of the strength it took to fulfill these orders, today, difficult and seemingly impossible tasks are sometimes called "herculean."