What six-headed monster does Odysseus encounter?

Scylla is the six-headed sea monster encountered by Odysseus in the Odyssey.

She lives on one side of a narrow sea passage, opposite Charybdis, the whirlpool monster. Circe warns Odysseus that he must sail close to Scylla because avoiding her by steering toward Charybdis could destroy the entire ship.

In Homer’s account, Scylla seizes six of Odysseus’s sailors—one with each of her heads—and devours them as the ship passes. Odysseus is unable to fight her or save the men, making the episode one of the poem’s bleakest examples of a leader forced to choose the lesser disaster.

Later Greek and Roman stories give Scylla different origins, often describing her as a beautiful nymph transformed into a monster through jealousy and magic. Charybdis is her counterpart, not an alternative name. Hydra is another many-headed monster, while Medusa is a Gorgon with snakes for hair.