Cronus was the leader of the Titans, the race before gods and ruled during the Golden Age.
Cronos was the son of Uranus, the Sky and Gaia, the Earth. He toppled his father and started ruling. Cronos kept on ruling the Earth until he was overthrown by his own son Zeus.
How did Cronos overthrow his father, and how was Cronos overthrown?
Uranus and Gaia had 3 sons called the Hecatoncheires, who had 100 hands and fifty heads. The Hecatoncheires were Briareus, Cottus, and Gyes. They also had 3 other sons, the Cyclopes, Arges, Brontes, and Steropes. Even though they had other offspring, Uranus despised only them and so he flung them into Tartarus where the wicked go after death where they are eternally punished. This enraged Gaia and so she asked the Titans to help overthrow Uranus, and then free the Hecatoncheires, and Cyclopes from Tartarus. Only, Cronos agreed to help Gaia though. After overthrowing Uranus, and becoming the ruler of the universe Cronos broke his promise and never rescued the Hecatoncheires or the Cyclopes.
It all started with a prophecy from the oracle at Delphi that Cronos would have 6 children and they would overthrow him. The oracle told Cronos that one day he would be overthrown by his own children. To prevent this, when Hades, Cronos's first child was born, Cronos swallowed him. Rhea was quite surprised when this happened, and when Poseidon was born, Cronos swallowed him, too. The same happened when Hera, Hestia, and Demeter were born. But the sixth time Rhea tricked Cronos into believing he had swallowed his sixth child, by presenting him with a rock wrapped in white cloth. Cronos was obviously happy knowing that his children could not cause him any harm. One day Rhea gave Cronos a concoction of herbs and told him those herbs would make him invincible and nobody would ever be able to dethrone him. Those herbs were a trick by Rhea though and those herbs made Cronus vomit out his children. After, that a war started between the Gods and the Titans, and the gods won. During the war, Zeus, Hades, and Poseidon went into the underworld and freed the Hecatoncheires and the Cyclopes. After the Gods won most of the Titans were sent into Tartus expect most female titans, and Prometheus and Epimetheus.