In Greek Myth
In Greek Mythology Cronos is the son of Gaia, the earth, and Oranos (also known by the Romanized version of the name, Uranus), the sky. He was the youngest of the 12 Titans which also includes: Oceanus, Tethy, Hyperion, Theia, Coeus, Phoebe, Rhea, Mnemosyne, Themis, Crius, Iapetus.
Ouranos was afraid of his children's powers so he hid them in Tartarus. Gaia was unhappy about this and asked one of the 12 to overthrow their father; only Cronos came forward. Cronos waited until his father was about to make love with Gaia and then lunged at Ouranos, castrating him with a sickle.
From this point on, Cronos and his wife Rhea (also his sister) would rule the heavens. Their rule became known as the "Golden Age" because the people lived without greed or violence and there was no need for laws. Cronos had five children with Rhea but was told by Gaia that one of them would overthrow him much like he had done to his father. To avoid this fate, Cronos ate all of this children alive as soon as they were born.
By the time Rhea had her 3rd son (Zeus), Gaia had become extremely concerned with the way Cronos had treated his children thus far, and so came up with a plan to save Zeus. She covered a rock with a cloth and gave it to Cronos. This tricked Cronos and he ate the rock thinking it was his son. Gaia, with the help of the goat Amalthea, would raise Zeus in Crete. Zeus would return and feed his father poison, making him regurgitate everyone that he had swallowed. A great war called Titanomachy broken out between the Gods and the Titans. In the end the gods were victorious and Cronos was banished to Tartarus.
In The God of War Series
In God of War it is discovered that Cronos has been sentenced to eternal punishment by Zeus for his crimes. The former king of the Titans is forced to wander the Desert of Lost Souls forever, while carrying the Temple of Pandora on his back. The games main character, Kratos, scales the Titan in order to enter the temple and claim Pandora's Box, a weapon that will allow him to defeat a god. Cronos however, seems unaware of Kratos' presence during the events of God of War.
In God of War II, Cronos is shown in cut scenes that explains the back story of a cyclical pattern of son overthrowing the father. Cronos, who defeated his father Uranus, is depicted swallowing all of his children in order to end the cycle, though Zeus is spared and raised by Gaia to eventually overthrow Cronos in the Titan war, with the aid of his brothers.
However, this is not the last time Cronos is mentioned in the second game. He later grants Kratos the last of his magic in the form of a lightening ability called Cronos' Rage, which was hidden in the giant statues called the Steeds of Time.