The Titans
The Titans, also known as the elder gods, are for many ages the supreme rulers of the universe. Known for their incredible size and strength, they rule the earth before the Olympians overthrew them. The ruler of the Titans is Cronus who is de-throned by his son Zeus. Most of the Titans fight with Cronus against Zeus and are punished by being banished to Tartarus. Eventually, however, Zeus is reconciled with the Titans, and Cronus is made ruler of the Golden Age. During their rule the Titans are associated with the various planets. 
Gaea 
Gaea, the Earth goddess, is one of the deities presiding over marriage and is regarded as all-producing and all-nourishing. She mates with her son Uranus to produce the remaining Titans. Gaea seems to have started as a neolithic earth-mother worshipped before the Indo-European invasion that eventually leads to the Hellenistic civilization. 
Uranus-king of the mountains
Gaea (Earth) with Chaos, produced Uranus, the Mountains and the Sea. From her union with Uranus is born the Titans and the Cyclopes. Uranus hates his children and hid them within Gaea's body. Gaea pleads with them to avenge her. Only the Titan Cronus obeys her. When Uranus approaches Gaea, Cronus springs upon him and cuts off his testicles. Some of the blood spatters on Gaea and from the blood is born the Furies and the Giants. The genitals are tossed into the sea producing a white foam from which is born Aphrodite.
Cronus 
Cronus is the ruling Titan who came to power by castrating his Father Uranus. His children by his wife, Rhea, are the first of the Olympians. To insure his safety, Cronus eats each of the children as they are born. This works until Rhea, unhappy at the loss of her children, tricks Cronus into swallowing a rock, instead of Zeus. When he grows up, Zeus revolts against Cronus and the other Titans, defeating them, and banishes them to Tartarus in the underworld. Cronus manages to escape to Italy, where he rulesas Saturn. The period of his rule is said to be a golden age on earth, honored by the Saturnalia feast.
Rhea-earth
She is a daughter of Uranus (Heaven) and Gaea (Earth). She marries her brother, Cronus. A prophecy told Cronus that one of his children would overthrow him, so to forestall that happening Cronus swallows his children as they are born. Those children are Hestia, Demeter, Hera, Hades and Poseidon. Rhea, finally, decides to fool Cronus and at the birth of her next child, Zeus, she presents Cronus with a large stone wrapped in blankets, which he, thinking it is Zeus, promptly swallows. As foretold, Zeus eventually overthrows Cronus, who is made to regurgitate the children he has swallowed. Rhea is also known as Agdistis.
Oceanus 
Oceanus is the unending stream of water encircling the world. Together with his wife Tethys, he produces the rivers and the three thousand ocean nymphs. 
Tethys 
Tethys is the wife of Oceanus. Together they produce the rivers and the three thousand ocean nymphs.
Hyperion 
Hyperion is the Titan of light, an early sun god. He is the son of Gaea and Uranus, the husband of his sister Theia, who bears their children Helius (the sun), Selene (the moon), and Eos (the dawn). 
Mnemosyne-memory 
She is the Titan goddess of memory. Zeus spends nine consecutive nights with her, after which, she gives birth to the nine Muses, one each day.
Themis 
Themis is the Titan of justice and order. She is the mother of the Fates and the Seasons.
Iapetus 
Iapetus is the father of Prometheus, Epimetheus, Menoetius, and Atlas by Clymene.
Coeus
Coeus is the Titan of Intelligence. Father of Leto.
Phoebe 
Phoebe is the Titan of the Moon. Mother of Leto.
Prometheus-forethought
The wisest Titan, and the creator of mankind. Originally a good friend and ally to Zeus, he later falls from favor (he supposedly tricks Zeus out of his share of a sacrificed ox), and is chained in the Caucasus Mountains where an eagle fed upon his "ever-regrowing" liver each day. He is credited with stealing fire from Hephaestus and giving it to the human race.
Epimetheus-afterthought 
Epimetheus, a stupid Titan, is the son of Iapetus. In some accounts he is delegated, along with his brother Prometheus by Zeus to create mankind. He also accepta the gift of Pandora from Zeus, which leads to the introduction of evil into the world. 
Atlas-he who dares
Son of the Titan, Iapetus, and the nymph, Clymene (Asia), and the brother of Prometheus. Atlas is one of the Titans that wars against Zeus, and lost. As punishment, Zeus condemns him to hold aloft the heavens forever. He is often pictured holding the earth on his shoulders.
Metis 
Metis, the Titaness of the forth day and the planet Mercury, presides over all wisdom and knowledge. She is seduced by Zeus and became pregnant with Athena. Zeus becomes concerned over prophecies that her second child would replace Zeus, so, to avoid, this Zeus eats her. It is said that she is the source for Zeus' wisdom and that she still advises Zeus from his belly. It may seem odd for Metis to have been pregnant with Athena yet never mentioned as her mother; the reason for this is that the classic Greeks believed that children are generated solely from the father's sperm. The woman is thought to be merely vessel in which the fetus grew. Since Metis is killed well before Athena's birth, her role doesn't matter much.