Uranus is the sky, and in Hesiod he is the sky in the most literal sense available: a thing with weight that rests on the earth. Gaia bears him without a partner, “equal to herself, to cover her on every side” — he is made as her covering — and then takes him as her consort. Everything that follows in the Theogony descends from that pairing: the twelve Titans, the three Cyclopes, and the three hundred-handed brothers.
He is also the first tyrant in Greek myth, and his tyranny is specifically a refusal to let a generation be born. As each child comes he pushes it back into a hiding place inside Gaia and will not let it into the light. The earth, crowded with her own unborn children, groans and makes a sickle of grey flint, and asks her sons which of them will use it. Only Cronus answers.
ἦλθε δὲ νύκτ᾽ ἐπάγων μέγας Οὐρανός, ἀμφὶ δὲ Γαίῃ ἱμείρων φιλότητος ἐπέσχετο καί ῥ᾽ ἐτανύσθη πάντη· ὃ δ᾽ ἐκ λοχεοῖο πάις ὠρέξατο χειρὶ σκαιῇ, δεξιτερῇ δὲ πελώριον ἔλλαβεν ἅρπην μακρὴν καρχαρόδοντα, φίλου δ᾽ ἀπὸ μήδεα πατρὸς ἐσσυμένως ἤμησε, πάλιν δ᾽ ἔῤῥιψε φέρεσθαι ἐξοπίσω
“And Heaven came, bringing on night and longing for love, and he lay about Earth spreading himself full upon her. Then the son from his ambush stretched forth his left hand and in his right took the great long sickle with jagged teeth, and swiftly lopped off his own father’s members and cast them away to fall behind him.” — Theogony 176–182, tr. Evelyn-White
The severance is what separates sky from earth — after it there is a gap for the world to happen in — and nothing thrown from it is wasted. The blood that falls on Gaia produces the Erinyes, the Giants and the ash-tree nymphs; the members, carried out to sea, gather foam and produce Aphrodite. Uranus names the Titans in the same breath, calling them Titēnes, “strainers”, because they strained to do a terrible thing and vengeance would come of it. He is right: Cronus will swallow his own children against exactly this outcome, and be deposed anyway.
What Uranus is not, is a god anyone worshipped. There are no temples to him, no festivals, no cult. He is a genealogical fact and a warning, a figure the poems need in order to explain where the Titans came from and why the sky is no longer lying on the ground. Compare the Egyptian arrangement, which runs the same cosmology with the sexes reversed: there the sky is Nut, a woman arched above, and the earth is Geb, a man lying beneath her, and the two are separated by their father Shu rather than by a son with a blade.
