In the beginning there was only chaos. Then out of the void appeared Erebus, the unknowable place where death dwells, and Night (Nyx). All else was empty, silent, endless, darkness. Then somehow Love (Eros ) was born bringing a start of order. From Love came Light and Day. Once there was Light and Day, Gaea, the earth appeared.
Then Erebus slept with Night, who gave birth to Aether, the heavenly light, and to Day the earthly light. Then Night alone produced Doom, Fate, Death, Sleep, Dreams, Nemesis, and others that come to man out of darkness.
Meanwhile Gaea alone gave birth to Uranus, the heavens. Uranus became Gaea's mate covering her on all sides. Together they produced the three Cyclopes, the three Hecatoncheires, and twelve Titans.
However, Uranus was a bad father and husband. He hated the Hecatoncheires. He imprisoned them by pushing them into the hidden places of the earth, Gaea's womb. This angered Gaea and she plotted against Uranus. She made a flint sickle and tried to get her children to attack Uranus. All were too afraid except, the youngest Titan, Cronus.
Gaea and Cronus set up an ambush of Uranus as he lay with Gaea at night. Cronus grabbed his father and castrated him, with the stone sickle, throwing the severed genitals into the ocean. The fate of Uranus is not clear. He either died, withdrew from the earth, or exiled himself to Italy. As he departed he promised that Cronus and the Titans would be punished. From his spilt blood came the Giants, the Ash Tree Nymphs, and the Erinyes. From the sea foam where his genitals fell came Aphrodite.
Cronus became the next ruler. He imprisoned the Cyclopes and the Hecatoncheires in Tartarus. He married his sister Rhea, under his rule the Titans had many offspring. He ruled for many ages. However, Gaea and Uranus both had prophesied that he would be overthrown by a son. To avoid this Cronus swallowed each of his children as they were born. Rhea was angry at the treatment of the children and plotted against Cronus. When it came time to give birth to her sixth child, Rhea hid herself, then she left the child to be raised by nymphs. To conceal her act she wrapped a stone in swaddling cloths and passed it off as the baby to Cronus, who swallowed it.
This child was Zeus. He grew into a handsome youth on Crete. He consulted Metis on how to defeat Cronus. She prepared a drink for Cronus design to make him vomit up the other children. Rhea convinced Cronus to accept his son and Zeus was allowed to return to Mount Olympus as Cronus's cupbearer. This gave Zeus the opportunity to slip Cronus the specially prepared drink. This worked as planned and the other five children were vomited up. Being gods they were unharmed. They were thankful to Zeus and made him their leader.
Cronus was yet to be defeated. He and the Titans, except Prometheus, Epimetheus, and Oceanus, fought to retain their power. Atlas became their leader in battle and it looked for some time as though they would win and put the young gods down. However, Zeus was cunning. He went down to Tartarus and freed the Cyclopes and the Hecatoncheires. Prometheus joined Zeus as well. He returned to battle with his new allies. The Cyclopes provided Zeus with lighting bolts for weapons. The Hecatoncheires he set in ambush armed with boulders. With the time right, Zeus retreated drawing the Titans into the Hecatoncheires's ambush. The Hecatoncheires rained down hundreds of boulders with such a fury the Titans thought the mountains were falling on them. They broke and ran giving Zeus victory.
Zeus exiled the Titans who had fought against him into Tartarus. Except for Atlas, who was singled out for the special punishment of holding the world on his shoulders.
However, even after this victory Zeus was not safe. Gaea angry that her children had been imprisoned gave birth to a last offspring, Typhoeus. Typhoeus was so fearsome that most of the gods fled. However, Zeus faced the monster and flinging his lighting bolts was able to kill it. Typhoeus was buried under Mount Etna in Sicily.
Much later a final challenge to Zeus rule was made by the Giants. They went so far as to attempt to invade Mount Olympus, piling mountain upon mountain in an effort to reach the top. But, the gods had grown strong and with the help of Heracles the Giants were subdued or killed.