Zeus was the youngest son of the Titans Cronus and Rhea. When he was born, his father Cronus intended to swallow him as he had all of Zeus's siblings: Poseidon, Hades, Hestia, Demeter and Hera. But Rhea hid the newborn in a cave on Mount Dicte in Crete. (To this day, the guides at the "cave of Zeus" use their flashlights to cast shadow puppets in the cave, creating images of baby Zeus from the myth.)
When he had grown up, Zeus caused Cronus to vomit up his sisters and brothers, and these gods joined him in fighting to wrest control of the universe from the Titans and Cronus, their king. Having vanquished his father and the other Titans, Zeus imprisoned most of them in the underworld of Tartarus.
Then he and his brothers Poseidon and Hades divided up creation. Poseidon received the sea as his domain, Hades got the Underworld and Zeus took the sky. Zeus also was accorded supreme authority on earth and on Mount Olympus.