Cassiopeia, in Greek legend, an Ethiopian queen. She was the wife of Cepheus and the mother of Andromeda. Cassiopeia boasted that her beauty surpassed that of the Nereids, or sea nymphs. The offended nymphs persuaded Poseidon, god of the sea, to punish Cassiopeia for her pride by sending a deluge and a sea monster to lay waste to the land.

At her death Cassiopeia was made a constellation of the northern sky. The constellation, also known as the Lady in Her Chair, contains 55 stars, the five brightest of them arranged in a sprawling W.