Argus Panoptes

Hundred-eyed giant set by Hera to guard the cow-shaped Io after Zeus's affair with her. The eyes never all closed at once — some slept while others kept watch — so no thief or lover could approach her unseen. Zeus dispatched Hermes, who lulled every eye to sleep with the music of his pipes and the long Argus-killing story, then struck off the giant's head. Hera gathered the hundred eyes and set them in the tail of her bird the peacock (Apollod. 2.1.3).