She was the wife of King Cepheus of Ethiopia and the mother of Andromeda. Cassiopeia was known for her great beauty, but she was also vain and arrogant. She boasted that she was more beautiful than the Nereids, the sea nymphs, which angered Poseidon, the god of the sea.
As punishment, Poseidon sent the sea monster Cetus to attack Ethiopia. To appease Poseidon and save her kingdom, Andromeda was chained to a rock as a sacrifice to the monster. However, she was rescued by the hero Perseus, who killed Cetus.
Cassiopeia was placed in the sky as a constellation, but her chair is tilted, signifying her eternal punishment for her vanity. She spends half of her time upside down, a constant reminder of her arrogance.
