Gaia

One of the first beings to come into existence, Gaia represents and IS the very earth. She has a rather complicated relationship with her direct descendants (specifically Uranus, Kronos, and Zeus), as she helps them rise to power only to turn against them soon after.



Tartarus

One of the first beings to come into existence, Tartarus represents and IS the stormy hellish pit far below the earth. He is most often used in myth to contain dangerous beings, a few of which he fathered.



Clotho



Lachesis



Atropos

The three Fates had complete control over the lives of every mortal: Clotho spun the thread of life for every being and thus had control over their births, Lachesis decided how long the threads were and chose how those lives would play out, and Atropos cut the threads and thus determined how every being's death would come about. While effectively the most powerful beings in Greek mythology, the Fates were obedient to Zeus (who, in some depictions, was their father).



Poseidon

One of the Twelve Olympians and ruler of the seas, Poseidon led an active life and played a part in many myths, not all of them strictly tied to the oceans. Among other things, Poseidon created horses, caused earthquakes, and chased women.