A major factor in the well-known tragedies surrounding Heracles is the hatred that the goddess Hera, wife of Zeus, had for him. A full account of Heracles must render it clear why Heracles was so tormented by Hera, when there were many illegitimate offspring sired by Zeus. Heracles was the son of the affair Zeus had with the mortal woman Alcmene. Zeus made love to her after disguising himself as her husband, Amphitryon, home early from war (Amphitryon did return later the same night, and Alcmene became pregnant with his son at the same time, a case of heteropaternal superfecundation, where a woman carries twins sired by different fathers).
Thus, Heracles' very existence proved at least one of Zeus' many illicit affairs, and Hera often conspired against Zeus' mortal offspring as revenge for her husband's infidelities. His twin mortal brother, son of Amphitryon, was Iphicles, father of Heracles' charioteer Iolaus.
On the night the twins Heracles and Iphicles were to be born, Hera, knowing of her husband Zeus' adultery, persuaded Zeus to swear an oath that the child born that night to a member of the House of Perseus would become High King. Hera did this knowing that while Heracles was to be born a descendant of Perseus, so too was Eurystheus. Once the oath was sworn, Hera hurried to Alcmene's dwelling and slowed the birth of the twins Heracles and Iphicles by forcing Ilithyia, goddess of childbirth, to sit crosslegged with her clothing tied in knots, thereby causing the twins to be trapped in the womb.
Meanwhile, Hera caused Eurystheus to be born prematurely, making him High King in place of Heracles. She would have permanently delayed Heracles' birth had she not been fooled by Galanthis, Alcmene's servant, who lied to Ilithyia, saying that Alcmene had already delivered the baby. Upon hearing this, she jumped in surprise, loosing the knots and inadvertently allowing Alcmene to give birth to Heracles and Iphicles.
Fear of Hera's revenge led Alcmene to expose the infant Heracles, but he was taken up and brought to Hera by his half-sister Athena, who played an important role as protectress of heroes. Hera did not recognize Heracles and nursed him out of pity. Heracles suckled so strongly that he caused Hera pain, and she pushed him away. Her milk sprayed across the heavens and there formed the Milky Way. But with divine milk, Heracles had acquired supernatural powers. Athena brought the infant back to his mother, and he was subsequently raised by his parents.
The child was originally given the name Alcides by his parents; it was only later that he became known as Heracles. He was renamed Heracles in an unsuccessful attempt to mollify Hera. He and his twin were just eight months old when Hera sent two giant snakes into the children's chamber. Iphicles cried from fear, but his brother grabbed a snake in each hand and strangled them. He was found by his nurse playing with them on his cot as if they were toys. Astonished, Amphitryon sent for the seer Tiresias, who prophesied an unusual future for the boy, saying he would vanquish numerous monsters.