Cronus was the master of all-devouring time, particularly eternity. He became king of the Titans when he overthrew his own father Uranus, castrating him with a magic sickle and throwing his genitalia into the ocean.
Even a master of time was not immune to fate, and Cronus had been told that he, like his own father, would be overthrown by a son. For that reason, he devoured all his children when they were born. His wife Rhea, however, tricked him into eating a stone instead of his son Zeus. When Zeus grew to adulthood, he returned and forced his father to disgorge the other children, then dethroned him and cast all the Titans into Tartarus.
Later, Cronus was released to rule over Elysium, the eternal realm of the blessed dead.