Which primordial deity personified the sky?

The primordial deity who personified the sky was Uranus.

Uranus, also written Ouranos, represented the overarching sky in Greek creation mythology. In Hesiod’s account, Gaia, the Earth, brought him forth and then became his consort. Together they produced the Titans, Cyclopes, and Hecatoncheires, making Uranus an ancestor of many major divine figures, including Cronus and the Olympian gods.

His most famous myth explains the succession of divine generations. Fearing the power of his children, Uranus confined some of them within Gaia. Gaia then urged Cronus to attack him with a sickle. After Uranus was overthrown, the Titans became the ruling generation. Greek myth also says that blood from the wound produced several beings, while Aphrodite arose from the sea foam associated with the severed divine flesh.

Uranus is not the same as Zeus: Zeus is an Olympian ruler and storm god, while Uranus is an earlier primordial embodiment of the sky. The Roman equivalent of Uranus was Caelus.