Metis Gaea
Gaea is the Earth goddess. She mated 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 lead to the Hellinistic civilization.
Uranus
Uranus is the sky god and first ruler. He is the son of Gaea, who created him without help. He then became the husband of Gaea and together they had many offspring, including twelve of the Titans.
His rule ended when when Cronus, encouraged by Gaea, castrated him. He either died from the wound or withdrew from earth
Cronus
Cronus was the ruling Titan who came to power by castrating his Father Uranus. His wife was Rhea. There offspring were the first of the Olympians. To insure his safety Cronus ate each of the children as they were born. This worked until Rhea, unhappy at the loss of her children, tricked Cronus into swallowing a rock, instead of Zeus. When he grew up Zeus would revolt against Cronus and the other Titans, defeat them, and banish them to Tartarus in the underworld.
Cronus managed to escape to Italy, where he ruled as Saturn. The period of his rule was said to be a golden age on earth, honored by the Saturnalia feast.
Rhea
Rhea was the wife of Cronus. Cronus made it a practice to swallow their children. To avoid this, Rhea tricked Cronus into swallowing a rock, saving her son Zeus.
Oceanus
Oceanus is the unending stream of water encircling the world. Together with his wife Tethys produced the rivers and the three thousand ocean nymphs.