Andromeda was the daughter of Cepheus and Cassiopeia, king and queen of the kingdom Ethiopia.
Her mother Cassiopeia boasted that she was more beautiful than the Nereids, the nymph-daughters of the sea god Nereus and often seen accompanying Poseidon. To punish the Queen for her arrogance, Poseidon, brother to Zeus and god of the Sea, sent a sea monster (Cetus) to ravage the coast of Ethiopia including the kingdom of the vain Queen. The desperate King consulted the Oracle of Apollo, who announced that no respite would be found until the king sacrificed his virgin daughter Andromeda to the monster. She was chained naked to a rock on the coast.
Perseus was returning from having slain the Gorgon Medusa, he found Andromeda and slew Cetus by turning him to stone. He set her free, and married her in spite of Andromeda having been previously promised to her uncle Phineus. At the wedding a quarrel took place between the rivals, and Phineus was turned to stone by the sight of the Gorgon’s head.
Perseus and Andromeda had seven sons: Perseides, Perses, Alcaeus, Heleus, Mestor, Sthenelus, and Electryon, and one daughter, Gorgophone. Their descendants ruled Mycenae from Electryon down to Eurystheus, after whom Atreus attained the kingdom, and would also include the great hero Heracles.
When she died, Andromeda was hung in the sky as a constellation. (x)