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.
Cassiopeia was a beautiful and prideful woman, who lusted after herself and power and she would do anything to keep hold of her power. Starting off as a figure of pride, her hubris was such that she offended the god Poseidon himself, who took it upon himself to humiliate her. She only cared about herself and would do anything to protect herself and her beauty, even murder and genocide. She did little to benefit her own people and she barely cared for them. She learned the hard way that selfish lust will only doom oneself. However, in an ironic twist of fate, she got her ultimate wish to stay beautiful by being transformed into stars.