In Greek mythology, Cyclops are giants with one eye in the middle of their forehead. Most often, we learn that the Cyclopes were descendants of Uranus (the god of the sky) and Gaia (the goddess of the earth). But other sources list Poseidon (god of the seas) as their father. And some sources say they were the sons of the Hekatoncheires.
The Cyclopes had their own nation and lived in a land called Hyperia, where they lived in caves. According to Hesiod, there were three of them - Steropes, Brontes and Arges.
The Cyclopes together sided with the god Zeus when he rebelled against his father Cronus. The Cyclopes forged thunder and lightning for Zeus, which enabled him to defeat his father. Next, the giants fashioned a helmet of invisibility, which they lent to Hades in his battle against the Titans. This helmet was then lent by Hades to the hero Perseus for his battle with Medusa. The Cyclopes also made a bow and arrows for the goddess Artemis. And they are said to have built the "Cyclopean walls" of Tiryns and Mycenae.
In Homer's Odyssey, Odysseus meets a cyclops named Polyphemos. This cyclops was blinded by Odysseus and was able to escape with his party from his island. Although he lost half his men.
The Cyclops was later killed by the god Apollo in retaliation for Zeus killing his son Asclepius with a lightning bolt made by the Cyclopes.