Gaia. She is the ancestral mother of all life: the primal Mother Earth goddess. She is the mother of Uranus (the sky) from whose 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.
Uranus wasn't thrilled about the offspring that he and Gaia had produced so he forced them back inside her. As one might expect she was less than pleased about this so she persuaded Cronos to castrate his father. Later she predicted that Cronos would be overthrown by one of his own children. As a precaution Cronos devoured all of his own offspring but his wife Rhea hid the infant Zeus from him. Later Zeus dethroned his father and became the leader of the gods of Olympus.
The concept of an earth mother is not exclusive to Greek myth. In Roman legend she is personified as Terra. The Sumerians honored Tiamet and the Maori people honored Papatuanuku the Sky Mother. Today many NeoPagans honor Gaia as the earth or as the archetypical embodiment of the Earth's power and energy.