Cassiopeia was queen of Ethiopia and an antagonist in the story of Perseus.
Cassiopeia once said she was the most beautiful woman on Earth and even goddesses were ugly compared to her. She incurred the wrath of Poseidon, who sent his pet monster after Ethiopia. The monster, a giant serpent, ate everyone it came upon. Cassiopeia cowardly put her own daughter Andromeda in the maws of the monster in order to appease it and protect herself, but Perseus came back from killing Medusa, and Perseus fought and killed the monster, thus scaring Cassiopeia. Perseus married Andromeda and Cassiopeia's treachery was revealed so Poseidon talked to Zeus and Zeus turned Cassiopeia into a distant constellation as punishment for her pride.