Gaia

Gaia is the ancient earth goddess also known as Mother Earth and mother of the Titans. She was the grandmother of the six elder Olympian Gods: Zeus, Poseidon, Hades, Hera, Demeter and Hestia. She sleeps deep beneath the Earth and dislikes anyone who disturbs her. She first appeared in the Hercules animated series episode Hercules and the Prince of Thrace.

Trivia

 * In the original myths Zeus, Poseidon and Hades, Hera, Demeter, Hestia and Amphitrite were among her grandchildren.
 * In the orignal myths Apollo, Ares, Hephaestus, Hermes, Triton, Otus and Dionysus, Aphrodite, Artemis, Athena, Persephone (and in some versions Nemesis) were among her great-grandchildren.
 * Hercules was her great-grandson and Megara her great-granddaughter-in-law as Hercules' wife, but both the grandmother and the grandchild didn't show any signs of recognition to each other.