Cronus envied the power of his father, the ruler of the universe, Ouranos. Uranus drew the enmity of Cronus's mother, Gaia, when he hid the gigantic youngest children of Gaia, the hundred-handed Hecatonchires and one-eyed Cyclopes, in Tartarus, so that they would not see the light. Gaia created a great stone sickle and gathered together Cronus and his brothers to persuade them to castrate Ouranos.
Only Cronus was willing to do the deed, so Gaia gave him the sickle and placed him in ambush. When Ouranos met with Gaia, Cronus attacked him with the sickle, castrating him and casting his testicles into the sea. From the blood that spilled out from Ouranos and fell upon the earth, the Gigantes, Erinyes, and Meliae were produced. The testicles produced a white foam from which the goddess Aphrodite emerged.
For this, Uranus threatened vengeance for overstepping their boundaries and daring to commit such an act. After dispatching Ouranos, Cronus re-imprisoned the Hecatonchires, and the Cyclopes and set the dragon Campe to guard them. He and his sister Rhea took the throne of the world as king and queen. The period in which Cronus ruled was called the Golden Age, as the people of the time had no need for laws or rules; everyone did the right thing, and immorality was absent.
However, when he married and bore children with Rhea, he learned from Gaia that he was destined to one day be overthrown by his own children. Since Cronus feared that one of his children would be his downfall, as he was that of his father before him, he decided that whenever one of his children was born, he would swallow it. Rhea could not stand another one of her children to be devoured until she was informed by Gaia to hide her final child in a cave, and replace him with a stone. Cronus blindly swallowed the stone, but gave him a painful stomach ache.
As the story goes, Zeus grows up, and plots against his father by literally slicing his stomach open and freeing his older siblings. Then frees the Cyclopes and Hecatonchires from Tartarus, gets aid from one of the Titans named Themis and her son Prometheus, and engages Cronus and the the rest of the Titans in the Titanomachy for ten years. Zeus defeats Cronus with a lightning bolt made by the Cyclopes as a show of gratitude. Zeus takes his Bronze Scythe and literally chops his father to pieces before casting them with the other Titans to Tartarus.