Gaia is the personification of the Earth, the daughter of Chaos, and one of the primordials. Gaia is the ancestral mother of all life: the primal Mother Earth goddess. She is the immediate parent of Ouranos (the sky), from whose sexual union she bore the Titans (themselves parents of many of the Olympian gods) and the Giants, and of Pontus (the sea), from whose union she bore the primordial sea gods.
Gaia conceived further offspring with Ouranos, first the giant one-eyed Cyclopes: Brontes ("Thunder"), Steropes ("Lightning") and Arges ("Bright"); then the Hecatonchires: Cottus, Briareos and Gyges, each with a hundred arms and fifty heads.
As each of the Cyclopes and Hecatonchires were born, Ouranos hid them in a secret place within Gaia, causing her great pain. So Gaia devised a plan. She created a grey flint sickle. And Cronus used the sickle to castrate his father Ouranos as he approached Gaia to have intercourse with her. From Ouranos' spilled blood, Gaia produced the Erinyes, the Giants and the Meliae. From the foam of Ouranos in the sea came forth Aphrodite.
Because Cronus had learned from Gaia and Ouranos that he was destined to be overthrown by one of his children, he swallowed each of the children born to him by his Titan sister Rhea. But when Rhea was pregnant with her youngest child, Zeus, she sought help from Gaia and Ouranos. When Zeus was born, Rhea gave Cronus a stone wrapped in swaddling-clothes in his place, which Cronus swallowed, and Gaia took the child into her care.
With the help of Gaia's advice, Zeus defeated the Titans. But afterwards, Gaia, in union with Tartarus, bore the youngest of her sons Typhon, who would be the last challenge to the authority of Zeus.