They were born to Gaea and Uranus. They were also the first smiths. When Cronus came to power he imprisoned the Cyclopes in Tartarus. The were released by Zeus and fought with him against the Titans. As a reward for their release the Cyclopes gave Zeus his weapons of lighting and thunder. They continued as his workers at Mount Olympus forging his thunderbolts
Apollo killed at least one of the Cyclopes to retribution for Zeus killing his son Asclepius