Cassiopeia (Greek: Κασσιόπεια) was a mythical queen consort of Aethiopia, wife of Cepheus, and mother of Andromeda.
Cassiopeia boasted that she and her daughter were more beautiful than all the sea nymphs. This brought the wrath of Poseidon, ruler of the sea, upon the land, and he sent a sea monster to attack the kingdom unless Andromeda was fed to the beast. The hero Perseus foiled Poseidon's plan by killing the monster and rescuing Andromeda.
Cassiopeia was eventually placed in the sky as a constellation; the myths disagree as to whether this was a punishment or a blessing.