Hercules, the son of Zeus and a mortal named Alcmene, married Megara, the daughter of King Creon of Thebes. When a neighbouring king named Eurystheus grew envious of Hercules’ authority, he challenged him to complete Twelve Labours, much to the pleasure of Zeus’ wife Hera (Juno). Although Hercules was reluctant, an oracle confirmed that the gods desired him to do as Eurystheus bade. They would reward him with immortality if he succeeded in the quest. Diodorus Siculus, a Greek historian of the first century BC from Sicily, describes the fiendish Labours in full.

Perseus (they say) was the son of Jupiter by Danaë, the daughter of Acrisius, and that Perseus begat Electryon of Andromeda, the daughter of Cepheus, and that Electryon begat Alcmena of Eurydice the daughter of Pelops, and that Jupiter (deceiving Alcmena) lay with her, and begat Hercules: so that by this genealogy Hercules descended from the chiefest of the gods, both immediately by his mother, and more remotely by his great grandfather Perseus. His virtue and valour were not only evident from his acts, but might be concluded and foreseen by what happened before he was born: for when Jupiter lay with Alcmena, he lengthened the night threefold, so that, spending so much time in procreating this child was a sign how extraordinary strong he was likely to be. They say that Jupiter lay not with her out of any amorous pang of love, as with other women, but merely for procreation sake: and therefore, willing that his embraces at this time should be lawful, he forbore all violence; and knowing that the woman’s chastity was such, that no arguments would prevail with her, he deceived her by taking upon him the shape of Amphitryon.

And now the time of her delivery drew nigh, when Jupiter, full of thoughts concerning the birth of Hercules, in the presence of all the gods declared, that he would make him king of the Persians, who was to be born that day. Whereupon Juno, enraged with jealousy, with the assistance of Ilithyia1 her daughter, gave a check to the delivery of Alcmena, and brought forth Eurystheus before his full time. But though Jupiter was thus outwitted by Juno, yet, that he might perform his promise, he took care to preserve the honour and reputation of Hercules; and therefore it is reported, that he prevailed with Juno to consent, that Eurystheus being made king according to his promise, Hercules, (who should be subject to him), performing twelve labours, (such as Eurystheus should impose upon him), should be taken into the society of the immortal gods.