Cronus was the King of the Titans, he grew afraid that his children would one day be stronger than him so he ate each of them straight after they were born.
While she was pregnant with his 6th child, she decided to trick him by giving him a stone wrapped in a blanket instead of the baby. He swallowed the stone without even realising. She then ran away to the island of Crete.
Zeus grew up on the island of Crete and was raised by a goat. After he became a young man, he came up with a plan to give his father a potion. Zeus' mother Rhea arranged for him to become his father’s cupbearer. He slipped the potion into a drink and made Cronos spit up his brothers and sisters.
The bothers and sisters then chose Zeus to become the leader of the Olympians. Cronos was afraid of Zeus. Cronus asked the Titans to join him to defeat Zeus and his siblings.
He was not able to get the Titan women to join him. Two of the men, Prometheus and Epimetheus actually joined the Olympians against their fellow Titans.
The rest of the Titan men chose Atlas to lead the battle against the Olympians.
For ten years, the Titans and the Olympians fought and neither side won. Gaia advised Zeus to free the Cyclopes and the hundred headed Giants from Tartarus (a place in the underworld) and convinced them to join his side.
Zeus went down to Tartarus, killed the monster which guarded the prisoners, and released them. In return for their freedom, the Cyclopes and the Giants joined forces with Zeus to make them more powerful.
The Cyclopes gave Zeus the power over thunder and lightning. Then the Cyclopes gave the helm of darkness to Hades and the trident to Poseidon. Hades used the helm of darkness to steal away Cronus’ weapons and Poseidon attacked him with the trident. In the confusion Zeus struck with lightning, and Cronus fell. With Cronus defeated and the added power of the Cyclopes and Giants, the Olympians were able to defeat the Titans.
The Titans who were in the war, were imprisoned in Tartarus. Atlas was given a special punishment for his role in the war. He was required to carry the earth on his shoulders for eternity. Then it was decided that Hades would be the ruler of the underworld, Poseidon would be the ruler of the sea and Zeus would be the ruler of the sky. Because the sky covers all the land he would be the supreme ruler of all.