What creature is a one-eyed giant in Greek mythology?

The one-eyed giant in Greek mythology is a Cyclops.

The Greek word Cyclops means “round-eye” or “circle-eye,” and Cyclopes are generally portrayed as giants with one eye in the middle of the forehead. Greek tradition contains more than one group of Cyclopes, so the familiar monster from adventure stories is only one version of the figure.

In Hesiod’s Theogony, the Cyclopes are three brothers—Brontes, Steropes, and Arges—who work as divine smiths. They forge Zeus’s thunderbolt, Poseidon’s trident, and Hades’ helmet of invisibility. Homer’s Odyssey instead presents a broader race of uncivilized, cave-dwelling shepherds, including Polyphemus, the giant blinded by Odysseus.

Cyclopes were also credited in later tradition with building the massive walls at Mycenae and Tiryns; these became known as “Cyclopean” masonry because later Greeks thought only giants could have moved the stones. A common mix-up is treating Cyclops as only Polyphemus: Polyphemus is one individual Cyclops, while Cyclopes is the plural name for the wider group.