Middle Kingdom onward, elaborated in the Graeco-Roman period
The eight of Hermopolis
Four frog-headed gods and four snake-headed goddesses, standing for the qualities of the water before there was anything.
The Ogdoad are four pairs, each pair a male frog and a female snake, and each pair a quality of the state before creation: the primordial water, boundlessness, darkness, and hiddenness or the unseen. They are not characters. They have no stories, no cults of their own to speak of, and no personalities; they are a way of describing an absence precisely.
From their interaction the primeval mound rises at Hermopolis, and on it either an egg or a lotus appears, from which the sun emerges. Which of the two depends on the version, and Egyptian sources do not treat the disagreement as needing resolution.
Where it comes from
Coffin Texts and later temple inscriptions
About this sourceThe fullest expositions are Graeco-Roman, at Hermopolis and at Esna, long after the idea itself appears.
What the story was for
The most abstract of the creation accounts, and the most philosophically interesting: it tries to say what was there before there was anything, and answers with four properties rather than four beings. The eighth member, hiddenness, is the one with a future. Amun, whose name means the hidden one, belongs to this group before he becomes the state god of an empire.
Other myths