After Love, Light, and Radiant Day came into existence, so did Mother Earth and Father Heaven, or Gaea and Ouranos.
They had 18 kids. 6 of them were ugly monsters who Ouranus unfairly imprisoned in a pit, and the other 12 were the Titans.
Gaea was mad that Ouranus imprisoned her kids, so she asked the eldest of the Titans, Cronus, to kill him. He took a scythe and, as his brothers held him down, he ripped good ol dad to shreds and took the crown. But after killing him, he still didn't release his hideous brothers.
King Cronus and his sister/wife Rhea then had 6 kids, but after being warned that one would one day rise up and kill him just like he had, he ate all 6 kids as they were born. Except for one, who Rhea replaced the 6th child with a rock.
Upon growing up and learning about his evil dad, Zeus gathered his hideous uncles and marched to the Titan palace, where he tricked Cronus into throwing up the kids and killed all of the evil Titans, and he let his uncles go free and he has ruled the heavens ever since