Epaphus was born from one of the oldest stories of desire, punishment and wandering in Greek mythology. His mother Io was a daughter of Inachus, the river god of Argos, and a priestess in the service of Hera, queen of the gods. Zeus desired her. When Hera discovered the affair, Io was transformed into a white heifer, in some tellings by Zeus as a disguise and in others by Hera as a punishment. Hera set Argus Panoptes, a giant whose hundred eyes never all slept at once, to watch the cow. Zeus sent Hermes, the god of travellers, thieves and messengers, to free her. Hermes lulled Argus to sleep with music and stories, cut off his head and led Io away. Hera answered by sending a gadfly to sting the heifer without rest.

The gadfly drove Io across the known world. She swam through the sea that took the name Ionian, crossed Illyria and the mountains of Thrace, passed the straits named the Bosporus, the Cow's Crossing, and wandered through Scythia and the land of the Cimmerians beside the Black Sea. In Aeschylus' Prometheus Bound, the chained Titan Prometheus sees her coming and reads her future. He tells her that she will cross still more lands and waters before reaching Canopus, the city at the silt-choked mouth of the Nile. There, he promises, Zeus will end her madness by the stroke and touch of his hand.

When Io reached Egypt, the central event of her son's story occurred. Zeus touched her, and the cow became a woman again. The child conceived and born from that touch was named Epaphus, Touch-born. Aeschylus calls him dark Epaphus, a son who would gather the fruits of the broad Nile and begin a line that would return to Greece many generations later. Another tradition moved his birth westward. Strabo placed it in the cave Boösaule on the island of Euboea, where the wanderer was said to have found shelter before reaching Egypt. Whether born beneath the Greek earth or beside the rising waters of the Nile, Epaphus carried two inheritances at once: the divine seed of Zeus and the suffering body of Io.

Hera's hatred did not end with his birth. In one account, she ordered the Curetes, the ecstatic shield-clashing guardians who had once protected the infant Zeus, to steal the child from his mother. Other storytellers gave the task to the Telechines, strange sea-demons skilled in metalworking and magic. The kidnappers carried Epaphus beyond Egypt and hid him among strangers. Zeus discovered the crime and destroyed the abductors, but the child had already vanished. Io searched for him as Demeter once searched for Persephone, crossing land and sea while the memory of the gadfly still burned in her. At last she found her son in Syria, nursed in the royal house of Byblos, and carried him back to the Nile.

Io married Telegonus, the king of Egypt in this extended version, and Epaphus grew up within the palace of the land that had given his mother refuge. He inherited more than a throne. The Greeks imagined him as the founder or early king of Memphis, the great city beside the Nile, and linked his name to the ancient royal city long before Greek armies crossed the Mediterranean. He married Memphis, a daughter of Nilus, the river god who personified the Nile, and by her he became the father of Libya. The land west of Egypt took its name from this daughter. Libya in turn lay with Poseidon, god of the sea, and bore Belus and Agenor. Belus became the father of the twin dynasties of Danaus and Aegyptus, while the descendants of Agenor carried the line into Phoenicia. Their children included Cadmus, the future founder of Thebes, and Europa, the princess carried away by Zeus in the form of a bull.

Thus a child born from a cow-shaped mother became the ancestor of kings, refugees and founders across the eastern Mediterranean. The fifty daughters of Danaus, the Danaides, traced their flight from Egypt back to Epaphus. So did Aegyptus and his fifty sons, whose forced marriage plot drove the Danaides back to Argos. In Phoenicia, Agenor's family produced Cadmus, Europa and their brothers, whose wanderings brought letters, cities and dynasties into Greek legend. Some fragments carried the genealogy still farther, making Epaphus the remote ancestor of Libyans, Ethiopians and even the tiny Pygmies who lived at the edge of the imagined world. His family tree became a map of how Greeks understood the deep connections between their own heroic age and the older kingdoms beside the Nile.

Epaphus also entered Greek myth through a fierce youthful rivalry with Phaethon, the son of Helios and the Oceanid nymph Clymene. Phaethon had grown up hearing that his father was the sun god, but other boys mocked the claim. Epaphus, himself protected by an unquestionable divine parentage, pressed the wound hardest. He taunted Phaethon for believing everything his mother said and for puffing himself up with an imagined father, the Lord of Day. Phaethon could not bear the doubt. He travelled east to the palace of the sun and begged Helios for proof. Helios swore by the Styx, the river of unbreakable oaths, to grant any request. Phaethon asked to drive the solar chariot for one day. The inexperienced boy lost control of the horses, scorched the earth, froze the sky and threatened to set heaven itself on fire. Zeus struck him down with a thunderbolt to save the cosmos. Epaphus never held the reins, but his insult helped push Phaethon towards them.

His own end came through Hera's jealousy. One late tradition sent Epaphus hunting, a king moving through the Egyptian reeds with horses, hounds and attendants. Somewhere in the marsh or desert, the chase became an ambush. Hera, unwilling to let the living proof of Zeus's affair rule a kingdom in glory, arranged for his death. The exact weapon changed with the teller, but the hand behind it remained the queen of the gods. Epaphus died as the son of Io had always been threatened, not for any crime of his own, but because he existed. His descendants preserved his bloodline and his cities, yet the child born from Zeus's touch could not escape Hera's reach.

The Greeks did not leave him only as a dead king. They joined his story to one of the most distinctive cults of Egypt. At Memphis, the Egyptians revered Apis, a sacred bull believed to be conceived when a flash of light from heaven fell upon a cow. The Apis was marked by a white sign upon its black forehead, an eagle-shaped marking upon its back, doubled hairs on its tail and the image of a scarab beneath its tongue. Greeks identified this divine bull with Epaphus and made Io the double of Isis, the Egyptian goddess who also could be shown with the horns of a cow. Aelian records the disagreement plainly: Greeks called Apis Epaphus and traced him from Io, while Egyptians claimed that Apis was older than the Greek wanderer and rejected the foreign family tree. The argument itself shows how completely Epaphus had crossed from Greek genealogy into Egyptian religion.

Herodotus placed the Apis at the centre of a terrible confrontation during the Persian conquest of Egypt. After Cambyses, king of Persia, had taken Memphis, the Egyptians began a festival to celebrate the discovery of a new Apis. Cambyses, believing that they were rejoicing at his own victory, demanded to see the god. When the priests brought out the calf, the Persian king drew his dagger and stabbed the sacred bull in the thigh, mocking the Egyptians for worshipping an animal. Herodotus reports that the Egyptians dressed the wound and the bull later died, whereupon Cambyses lost his mind and committed further outrages. The story joined a Persian king, an Egyptian bull and a Greek account of sacrilege. Behind the sacred animal stood the Greek memory of Epaphus, son of Zeus and Io.

Epaphus survives less as a fully drawn character than as a hinge upon which myth turns. His birth closes Io's suffering and opens the history of Egypt. His daughter Libya gives a name to Africa. His grandchildren carry Greek myth into Phoenicia, Argos and Thebes. His insult sets Phaethon on the path to the sun. His identification with Apis turns Greek legend towards Egyptian animal worship. Aeschylus used his genealogy to explain why the Danaides could claim Argos as their ancestral home and why Heracles, a distant descendant, would one day free Prometheus. Every branch of the family tree carries the same beginning: a queen's jealousy, a girl transformed into a heifer, a gadfly's sting and a god's restorative touch. From that touch came a king, a bull and a map of the mythic world.