The Cyclopes were almost like human beings but of a gigantic size and with only one eye in the middle of their heads. Essentially there were three of them: Brontes (thunderer), Steropes (Lightener), and Arges (Bright).
They were born to Gaea and Uranus.
The Cyclopes were the first smiths. Volcanos were believed to be the aftermath of their underground work.
When Cronus came to power he imprisoned the Cyclopes in Tartarus. They 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.
Polyphemus, (son of Poseidon), is the most popular cyclops. He fighted with Odysseus that came out victorious, and left Polyphemus, blinded.
Hermes killed Arges while he guarded Io for Hera. Apollo also killed at least one of the Cyclopes to retribution for Zeus killing his son Aesculapius.