Argus Panoptes was born from the earth itself, or so the earliest accounts tell it. Gaia, the primordial goddess who is the living earth, brought him forth without father, an autochthon, one of those beings who spring directly from the soil they will one day guard. Other stories name different parents: some say he was the son of Arestor, a lord of the Argolid, and the nymph Mycene, after whom the great city of Mycenae was named; others call him a descendant of Inachus, the river-god whose waters flow through the plain of Argos. Wherever he came from, Argus was a giant of terrible strength and extraordinary vigilance. His epithet Panoptes means all-seeing, and in the earliest telling by Hesiod, the poet said that Argus had four eyes so that he could look in every direction at once, and that the goddess Hera, the wife of Zeus and queen of Olympus, had filled him with unwearying strength so that sleep never fell upon him. In later ages, as the Greeks grew more literal in their imagination, those four eyes became a hundred, spread across his gigantic head and body so that while some eyes slept, others remained forever awake, and no approach could escape his notice.

Before Hera claimed him, Argus had already made a name for himself as a slayer of monsters and a righter of wrongs. In Arcadia, the mountainous heart of the Peloponnese, a fierce bull had gone mad and was ravaging the countryside, goring herdsmen and trampling crops. Argus hunted the beast down and killed it, clothing himself in its hide as a trophy of his strength. He also ambushed and slew a satyr who had been robbing and violating travellers on the roads, a creature of the wild that had grown bold enough to prey upon civilised men. His greatest feat, according to the mythographer Apollodorus, was the killing of Echidna, the monstrous daughter of Tartarus, the pit beneath the world, and Gaia herself. Echidna was half beautiful woman and half writhing serpent, and she had made her home in a cave from which she kidnapped and devoured any traveller who passed too close. Argus waited until she slept and then struck, ridding the roads of one of the most feared creatures in Greece. He also avenged the murder of Apis, a king of the Argolid, tracking down the killers Thelxion and Telchis and delivering justice with his own hands.

These deeds brought Argus to the attention of Hera, who needed a guardian of absolute loyalty and absolute vigilance. Her husband Zeus, the king of the gods whose thunderbolt shook the heavens, had fallen in love with Io, a beautiful priestess who served in Hera's own temple at Argos. When Hera discovered the affair, Zeus tried to hide his lover by transforming her into a sleek white heifer, claiming that the earth had brought forth the cow. Hera was not deceived, but she pretended to be charmed by the animal and asked Zeus to give it to her as a gift. Trapped by his own lie, Zeus could not refuse without revealing the truth. Hera took the heifer and tethered her to an olive tree in the sacred grove of the Argive Heraion, and then she sent for Argus Panoptes. The giant arrived and took up his post, his hundred eyes gleaming in all directions, watching Io by day as she grazed and by night as she lay chained upon the ground. No matter which way he turned, some eyes always faced the heifer, and some eyes always scanned the horizon for rescue. He was the perfect gaoler, and Io, who could still think and feel beneath her bovine form, could only low in despair and wait.

Zeus, unable to approach Io himself without alerting his wife, turned to Hermes, his son by the Pleiad nymph Maia, the messenger of the gods who wore winged sandals and carried a wand that could charm any creature to sleep. Hermes flew down from Olympus to the grove of the Heraion, removed his cap and wings, and disguised himself as a shepherd driving a flock of goats. He approached Argus and asked if he might rest in the shade, and the giant, lonely and bored with his endless watch, agreed. Hermes began to talk, telling stories that meandered in circles, and then he took out his reed pipes and played a soft, repetitive melody. One by one, Argus's eyes began to droop. The giant fought to stay awake, asking Hermes about the pipes and how such an instrument had been invented, and Hermes told him the tale of Pan and the nymph Syrinx, a story of pursuit and transformation that seemed to go on forever. By the time the tale was done, every one of Argus's hundred eyes had closed in sleep. Hermes drew his sword and struck off the giant's head in a single blow, spattering the rock with blood. From that day forward, Hermes bore the epithet Argeiphontes, the Slayer of Argus, and the death of the hundred-eyed giant was said to be the first blood spilled among the new generation of Olympian gods.

Hera found her faithful watchman dead at dawn and was overcome with grief and rage. She took his hundred eyes and set them into the tail feathers of the peacock, the bird that became her sacred symbol, so that Argus's vigilance would never be lost to the world. In the shimmering eyes of the peacock's tail, the Greeks saw the gleam of the giant who had never slept, a memorial more beautiful than any tomb. As for Io, Hera sent a stinging gadfly to torment her, driving the heifer-maddened priestess across the earth, through the Ionian Sea that would bear her name, and all the way to Egypt, where she would at last regain her human form and bear Zeus a son. But the story of Argus endured. The Greeks of Argos worshipped him as a hero, and artists painted his death upon their vases for centuries: Hermes with his sword raised, Argus with eyes already closing, and the white heifer watching from the edge of the scene. The very idea of the all-seeing guardian passed into language and philosophy; the word panopticon, coined millennia later to describe a prison in which every inmate is visible to a single watchman, carries the echo of Argus in its name.