Queen Hera was the wife of Zeus and the peacock is one of her sacred animals, because his iridescent wings have an eye on them, a symbol of her vigilance. According to the legend, when Zeus met Io, he was stunned by her beauty and in order to spend some time with her, he covered the earth with a dense cloud, so that she could not escape.
Hera began to suspect the betrayal when she did not find her husband and after seeing the cloud. Zeus transformed Io into a cow to hide her from Hera, but while his wife found out about his trick, she pretended not to recognize her.
She asked him to give the cow to her and she assigned her servant, Argos Panoptis (meaning the one who sees everything), a beastly creature with a hundred eyes, to guard her, so that she would not meet Zeus.
But the king of the gods took pity on the poor girl and ordered Hermes to kill Argos and set her free. The winged god approached Argos singing and playing the flute to put him to sleep. When all of Argos’ eyes were closed, Hermes drew his sword and cut off his head. After the murder, Hera scattered the eyes of her faithful servant on the peacock’s plumage and the unique pattern of his tail emerged.
To punish Io, however, she sent her an Erinya, a goddess of vengeance and retribution, who disturbed her soul and made her wander the streets like crazy. Zeus, again regretting the girl’s downfall, apologized to Hera, who finally agreed to end her suffering.