Cassiopeia (classical Greek: Κασσσιόπεια, "Κασσσιέπεια", "Κασσσώπη" or "Κασσσιόπη"), in Greek mythology, was married to Cepheus, king of Ethiopia, and mother of the princess Andromeda.
Cassiopeia was vain and arrogant, even proclaiming herself more beautiful and better than the Nereids (another version told that the compliment would have been directed to her daughter, Andromeda).
Being the wife of Poseidon, Amphitrite, one of the Nereids, felt offended and asked the god of the seas to punish the queen for her boldness. Poseidon then sent a sea monster to destroy the kingdom of Cepheus.
The oracle of Ammon announced to the king that the monster would only be placated if they offered Andromeda as a sacrifice, so the princess was chained to a rock, but Perseus saw her and fell in love with her.
Perseus said he would kill the monster and set her free if she were given in marriage; but during the marriage, because Andromeda was promised to her uncle Phineus, the latter plotted against Perseus, and was turned to stone, along with his companions, by the sight of Medusa's head.
Not to escape punishment unscathed, Cassiopeia was transformed into the constellation that bears her name so that she spent most of her time turned upside down.
According to John Tzetzes and Euripides, the story of Andromeda took place in Joppa, and by the time of Flavius Josephus, there were in Joppa remnants of the chains that bound the princess.
Cassiopeia's parents are not named in the ancient texts, but Adolf Bastian conjectured that Cassiopeia would be the daughter of Phoenix, the son of Agenor, and Cassiopeia, the daughter of Arabo.
Phineus, Andromeda's uncle and fiancé, whom Pseudo-Apolodorus indicates as the brother of Cepheus, would be another son of Phoenix and Cassiopeia, the daughter of Arabo. Other children of this marriage would be Cilix and Doriclus, in addition to Atymnius, whose father was actually Zeus.
Luís de Camões refers to her in the Lusiads (X, 88), with the verse "See from Cassiopeia the fermosura."