Epimetheus was born in the generation before the Olympian gods, when the Titans ruled the cosmos under the tyranny of Cronus, the father of Zeus who had swallowed his own children to prevent a prophecy of overthrow. His father was Iapetus, one of the primordial deities who held the pillars that separated heaven and earth, and his mother was Clymene, one of the three thousand daughters of Oceanus and Tethys, the ancient gods of the sea. His brothers were Atlas, who would later stand at the western edge of the world holding up the broad sky; Menoetius, whose reckless pride would earn him a thunderbolt from Zeus; and Prometheus, whose cleverness and foresight would make him the champion of mankind and the enemy of the king of the gods. From the beginning, the two middle brothers were opposites. Prometheus looked ahead, planned, calculated, and schemed. Epimetheus looked behind, forgot, acted on impulse, and only understood his mistakes when it was too late to undo them. Their names were their natures: forethought and afterthought, the planner and the one who makes excuses.

When the Olympian gods under Zeus had defeated the Titans and established their new order, they turned their attention to the earth and its creatures. Prometheus and Epimetheus were given the task of creating the animals and populating the world with living things. The gods gave them a store of qualities and attributes - strength, speed, cunning, fur, feathers, claws, shells, horns - and told them to distribute these gifts among the creatures they fashioned from earth and water. Epimetheus, eager and impulsive, took charge of the distribution while Prometheus was busy with the greater work of shaping mankind. He gave strength to the lion, swiftness to the deer, the ability to fly to the eagle, a thick shell to the tortoise, venom to the serpent, wings to the butterfly, and a keen sense of smell to the dog. He gave every creature some defence, some advantage, some gift that would allow it to survive in the world. He worked quickly and with enthusiasm, and when he had finished he looked around with satisfaction at the rich diversity of the animal kingdom. Then Prometheus came to him and asked what gift remained for mankind, the creature he had shaped with his own hands in the image of the gods. Epimetheus's heart sank. He had given everything away. There was no swiftness left, no strength, no claws, no fur, no shell, no venom. Mankind stood naked, defenceless, and slow, the only creature on earth without a natural gift to protect it.

Prometheus, seeing the disaster his brother had created, knew that mankind could not survive as they were. He turned to the gods and asked for fire, the divine element that would give humans the power to cook their food, forge their tools, warm their homes, and light their way through the dark. But Zeus, the king of the gods who had already been tricked by Prometheus at the feast of Mekone, where the Titan had divided the sacrificial ox and given the gods the bones wrapped in fat while keeping the meat for mankind, refused. Fire was the property of the gods, and Zeus would not share it with creatures who were already, in his view, a mistake. So Prometheus, the forethinker, devised a plan. He climbed Mount Olympus by night, crept into the forge of Hephaestus, the divine smith whose limping gait and broken feet were the result of being thrown from heaven by Zeus, and took a spark of fire in a hollow fennel stalk. He carried it down to earth and gave it to mankind, and with that gift humanity began to build cities, forge weapons, and grow strong enough to challenge the very gods who had made them.

Zeus was furious. He had been outwitted by Prometheus twice, and he would not be outwitted a third time. He devised a punishment that would strike not at Prometheus directly, but at the creatures Prometheus loved. He ordered Hephaestus to mould a woman from earth and water, a creature of surpassing beauty, and then he commanded every god on Olympus to give her a gift. Athena, the goddess of wisdom and war, taught her to weave and clothed her in shimmering garments. Aphrodite, the goddess of love, gave her beauty and desire. The Graces gave her golden necklaces, and the Seasons crowned her with spring flowers. Hermes, the messenger of the gods, gave her a shameless mind, a deceitful nature, and the power of speech. Zeus named her Pandora, which means all-gifted, because every god had given her something, and though the name sounded like a blessing it was in truth a curse. She was a plague designed for mankind, a beautiful trap wrapped in silver and gold.

Before she was sent down, Prometheus came to his brother with a warning. He told Epimetheus, in the clearest possible terms, never to accept a gift from Olympian Zeus. Send it back, he said. Do not bring it into your house, or I fear that mortals will suffer for it. But Epimetheus, whose nature was to act first and consider later, whose heart was moved by beauty and whose mind was not made for suspicion, forgot the warning as soon as he saw Pandora. When Hermes brought her to the earth and presented her to Epimetheus as a bride, the Titan accepted her gladly. He took her into his home, and for a time they lived together, and she bore him a daughter named Pyrrha, whose name means fiery-red, a girl who would one day become the ancestress of the human race.

But Pandora had brought with her a jar, a pithos of baked clay, sealed and heavy, which the gods had told her never to open. Curiosity, the gift that Hermes had planted in her mind, grew stronger every day. She looked at the jar and wondered what treasure it contained. Perhaps jewels, perhaps nectar, perhaps some secret of the gods that would make her even more wonderful than she already was. One day, when Epimetheus was away, she lifted the heavy lid. What flew out was not treasure but terror: ten thousand sorrows, diseases, pains, toils, and plagues that scattered across the earth like a swarm of wasps. Before that moment, mankind had lived without sickness, without hard labour, without the grief that ages the body before its time. Now all of those evils were loose, and they have never been recalled. Pandora slammed the lid down, but too late. Only one thing remained inside, caught beneath the rim: Elpis, Hope, the one consolation that keeps mortals from despair. Some say hope is a blessing, the last gift of the gods that allows men to endure their suffering. Others say it is the cruellest evil of all, a false promise that keeps them struggling when they should accept their fate. Either way, it was all that Epimetheus's forgetfulness had left them.

The consequences of Epimetheus's mistake did not end with the jar. Zeus, still furious at Prometheus, had the Titan chained to a rock in the Caucasus Mountains, where every day an eagle tore out his liver and every night it grew back, an eternal torture that only ended when Heracles, the greatest hero of Greece, shot the eagle and broke the chains. But Epimetheus was not punished directly. He lived on, married to the woman he had welcomed, and raised his daughter Pyrrha. When the great flood came, sent by Zeus to destroy the wicked race of the Bronze Age, Pyrrha and her husband Deucalion, who was the son of Prometheus, were the only two mortals to survive. They landed their ark on Mount Parnassus and, following the instructions of the goddess Themis, cast stones behind them that became the new race of men and women. From Pyrrha, the daughter of Epimetheus and Pandora, the human race was reborn. In some later accounts, Epimetheus had another daughter named Metameleia, whose name means regret of what has occurred, a personification of the sorrow that comes to those who do not plan ahead. The poet Pindar called him the father of Prophasis, the goddess of Excuse, the word that follows every failure of foresight. And a scholion on the Argonautica records that some said his wife was not Pandora at all but Ephyra, a daughter of Oceanus and Tethys, though this tradition never replaced the story of Pandora in the popular imagination.