In Greek mythology, Argus (Argos) Panoptes—"all-seeing Argos"—was the many-eyed watchman whom Hera set to guard Io in heifer form. Ancient accounts give him from four to a hundred eyes, never all asleep at once. Hermes, sent by Zeus, lulled him and killed him; Hera set his eyes in the peacock's tail. Distinct from other figures named Argus (the Argonaut builder, Odysseus' dog, and others).
Adapted from Wikipedia, "Argus Panoptes" · CC BY-SA 4.0
I.Parentage and the watchman
Genealogies disagree: Apollodorus makes him son of Arestor; others name Inachus, Argus and Ismene, or call him earth-born from Gaia. A Hesiodic fragment already describes a great watcher with four eyes whom sleep never wholly overcomes; later art and Ovid's hundred eyes make the vigilance literal—some eyes always stay awake.
Hera charged him to tether the white heifer Io to a sacred olive at the Argive Heraion (or Nemea). Apollodorus also credits him with earlier feats: slaying a bull that ravaged Arcadia and, in one tradition, killing the monster Echidna as she slept.
II.Death and the peacock
To free Io, Zeus sent Hermes. Disguised as a shepherd, Hermes charmed Argus to sleep with story and pipe (or closed his eyes with the wand), then beheaded him—or, in other versions, struck him with a stone. The killing earned Hermes the epithet Argeiphontes, "Argus-slayer."
Hera preserved her servant's eyes in the peacock's plumage; some tellings transform Argus himself into the bird. Io, freed but tormented by Hera's gadfly, wandered until she reached Egypt. The episode is a favorite of classical and later painters.