The wife of Cepheus, mother of Andromeda, and queen of Ethiopia. She boasted that she, or her daughter, was more beautiful than the Nereids. The Nereids complained to Poseidon and the god sent a sea-monster to devastate Cepheus' kingdom. An oracle told Cepheus that by sacrificing his daughter the country would be rid of the monster, and so he had the girl chained to a rock near the ocean. When the hero Perseus returned from his quest to bring back the head of Medusa, he saw Andromeda and fell in love with her. He bargained with Cepheus for her hand in marriage if he succeeded in killing the monster and Cepheus gave his consent. Perseus kills the monster, Cepheus and Cassiopeia rejoice, and Perseus claims Andromeda as his bride (Metamorphoses IV, 663-803).
After death, Cassiopeia was placed among the stars, situated between the constellations Cepheus and Andromeda. However, because of the enmity between her and the Nereids and to teach her a lesson in humility, they had her placed in that part of the heaven near the pole where every night she is half the time held with her head downward.