Rhea is the Titaness daughter of the earth goddess Gaia and the sky god Ouranos, in Greek mythology and sister and wife to Cronus. She is known as "the mother of gods" and therefore is strongly associated with Gaia. The classical Greeks saw her as the mother of the Olympian goddesses and gods, but not as an Olympian goddess in her own right.
Cronus sired six children by Rhea: Hestia, Hades, Demeter, Poseidon, Hera, and Zeus in that order, but swallowed them all as soon as they were born except Zeus, since Cronus had learned from Gaia and Ouranos that he was destined to be overcome by his own child as he had overthrown his own father. When Zeus was about to be born, however, Rhea was unable to bare another loss and sought Ouranos and Gaia to devise a plan to save him, so that Cronus would get his retribution for his acts against Ouranos and his own children. Rhea gave birth to Zeus in Crete, handing Cronus a stone wrapped in swaddling clothes, which he promptly swallowed.
This act allowed Zeus to rebel against the Titans and thus be the cause of their downfall. Zeus forced Cronus to disgorge the other children in the reverse order in which they had been swallowed, the oldest becoming the last, and youngest: first the stone, which was set down at Pytho under the glens of Parnassus to be a sign to mortal men, then the rest. In some versions, Metis gave Cronus an emetic to force him to disgorge the babies, or Zeus cut Cronus' stomach open. Then Zeus released the brothers of Cronus, the Gigantes, the Hecatonkheires, and the Cyclopes, who gave him thunder and lightning, which had previously been hidden by Gaia. Zeus and his siblings, together with the Gigantes, Hecatonkheires, and Cyclopes, overthrew Cronus and the other Titans.