While Hercules was yet a newborn infant, wise and wily Athena duped Zeus' wife Hera, Queen of the Olympians, into breastfeeding the infant boy and thus, inadvertently and unknowingly, bestowing invulnerability upon him through her divine milk. Alcmena gave birth to the baby boy who would one day come to be known as Hercules.
To accomplish this goal, Zeus came to and seduced the mortal Queen Alcmena in the guise of her husband, King Amphitryon of Troezen. Recognizing the need for a champion who would be powerful enough to defend both the Olympian gods and humanity from future dangers she foresaw, Athena, the Goddess of Wisdom, arranged for her father Zeus to sire a half-mortal son to be that champion.
Hercules is the son of Zeus, Sky-father and supreme ruler of the gods of Olympus, and Alcmena, a mortal woman who lived over three thousand years ago.