Aten did not begin as a god. In the Old Kingdom, around 2600 BCE, the word jtn simply meant "disc," any flat and circular object, and the sun was called the "disc of the day" where Ra, the great sun god, was thought to reside. The first known reference to the Aten as a deity appears in The Story of Sinuhe, a tale from the Twelfth Dynasty around 1985 BCE, in which the deceased king Amenemhat I is described as rising to the heavens and "uniting with the sun-disk, the divine body merging with its maker." For centuries the Aten remained a minor aspect of the solar cult, a symbol of the visible sun rather than a god in his own right, overshadowed by Ra, Amun-Ra, and the falcon-headed Horus of the horizon.

The transformation began under Amenhotep III, the pharaoh of the Eighteenth Dynasty who ruled Egypt during its golden age and built the great temples at Luxor and Karnak. Amenhotep elevated the Aten to prominence, depicting the solar disc with a falcon head like Ra and making it the preeminent creator deity of a pantheon that still included the old gods. But it was his son, Amenhotep IV, who would shatter three thousand years of tradition. In the fifth year of his reign, around 1348 BCE, the young pharaoh changed his name to Akhenaten, meaning "Effective for the Aten," and declared that the sun disk was the sole god of Egypt. He abandoned Thebes, the city of Amun-Ra and the centre of Egyptian religion for centuries, and founded a new capital in the desert called Akhetaten, the Horizon of the Aten, on a bend of the Nile where nothing had stood before.

The defining text of Atenism is the Great Hymn to the Aten, carved across thirteen columns of hieroglyphic text in the tomb of Ay at Akhetaten. The hymn is a radical departure from everything that had come before. It declares that the Aten is the only god, the creator of all countries and peoples, the giver of life to every creature that walks, swims, or flies. It describes how the disk rises each morning and fills the world with light, how its rays reach down like hands to touch and sustain the living, how it creates the Nile in the sky as rain for foreign lands while the river itself flows for Egypt. It paints a picture of a world that falls silent and dies when the sun sets, where lions and serpents roam in the darkness because the forces of chaos are unleashed when the Aten is absent. For Akhenaten, there was no underworld journey, no battle with Apep the serpent of chaos, no regeneration through Osiris, the god of the dead and resurrection. When the sun set, the world simply stopped, and only the return of the disk at dawn could restore life.

The temples of the Aten were unlike anything Egypt had ever built. They had no roofs, no dark inner sanctuaries, no statues of the god hidden behind veils. They were open to the sky, vast courtyards of offering tables and altars where the sun could shine unobstructed upon the worshippers. No idols were permitted, for Akhenaten declared that the Aten could not be captured in stone or wood, and the only image allowed was the rayed solar disc itself, its rays ending in human hands that reached down to anoint the king and his family with the ankh, the breath of life. The royal family - Akhenaten, his chief wife Nefertiti, and their six daughters - became the sole intermediaries between the god and the people. The rays of the sun only held out life to the king and queen, and the common people received their blessing through them. Priests had little to do, for there were no divine images to clothe and feed, no oracles to interpret, and no barque processions to carry through the streets. Instead, the royal family rode in chariots on festival days, and elite women worshipped in sun-shade temples that caught the light without exposing them to its full glare.

The revolution did not last. Akhenaten died around 1336 BCE, and his successors moved quickly to undo what he had done. The boy king who followed him, originally named Tutankhaten, changed his name to Tutankhamun and abandoned Akhetaten for Thebes. He reopened the temples of Amun-Ra, restored the old priesthoods, and erased Akhenaten's name from the monuments. The city of Akhetaten was dismantled, its stone blocks reused for other buildings, and the name of the heretic king was chiselled from every inscription in a campaign of damnatio memoriae that sought to erase him from history. The Aten returned to what he had been before: a symbol, a disc, an aspect of the sun rather than its sole master. Yet the hymn survived, buried in the sand of Amarna, and when archaeologists uncovered it in the nineteenth century, they found a text so beautiful and so radical that it has been compared to Psalm 104 of the Hebrew Bible, a poem that some scholars believe may have been influenced by Akhenaten's revolution.