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 invasions that eventually lead to the Hellenistic civilization.
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 Cronus, encouraged by Gaea, castrated him. He either died from the wound or withdrew from earth.
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 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 is the unending stream of water encircling the world. Together with his wife Tethys produced the rivers and the three thousand ocean nymphs.
Tethys is the wife of Oceanus. Together they produced the rivers and the three thousand ocean nymphs.
Hyperion is the Titan of light, an early sun god. He is the son of Gaea and Uranus. He married his sister Theia. Their children Helius (the sun), Selene (the moon), and Eos (the dawn).
Mnemosyne was the Titan of memory and the mother of Muses.
Themis was the Titan of justice and order. She was the mother of the Fates and the Seasons.
Iapetus was the father of Prometheus, Epimetheus, Menoetius, and Atlas by Clymene.
Coeus is the Titan of Intelligence. Father of Leto.
Phoebe is the Titan of the Moon. Mother of Leto.
Prometheus was the wisest Titan. His name means "forethought" because he was able to foretell the future. He was the son of Iapetus. When Zeus revolted against Cronus, Prometheus deserted the other Titans and fought on Zeus side. By some accounts he and his brother Epimetheus were delegated by Zeus to create man. In all accounts, Prometheus is known as the protector and benefactor of man. He gave mankind a number of gifts including fire. He also tricked Zeus into allowing man to keep the best part of the animals sacrificed to the gods and to give the gods the worst parts. For this Zeus punished Prometheus by having him chained to a rock with an eagle tearing at his liver. He was to be left there for all eternity or until he agreed to disclose to Zeus which of Zeus children would try to replace him. Heracles eventually rescued him without giving in to Zeus.
Epimetheus was a stupid Titan, whose name means "afterthought". He was the son of Iapetus. In some accounts he is delegated, along with his brother Prometheus by Zeus to create mankind. He also accepted the gift of Pandora from Zeus, which lead to the introduction of evil into the world.
Atlas was the son of Iapetus. Unlike his brothers Prometheus and Epimetheus, Atlas fought with the other Titans supporting Cronus against Zeus. Due to Cronus's advance age Atlas lead the Titan's in battle. As a result he was singled out by Zeus for a special punishment and made to hold up the world on his back.
Metis was the Titaness of the forth day and the planet Mercury. She presided over all wisdom and knowledge. It is said that she is the source for Zeus wisdom and that she still advises Zeus from his belly. She was seduced by Zeus and became pregnant with Athena. Zeus became concerned over prophecies that her second child would replace Zeus. Since Metis was killed well before Athena's birth her role doesn't count.