Andromeda is a princess of Ethiopia, daughter of Cepheus and Cassiopea. Her mother offended the gods by boasting that the girl was more beautiful than the Nereids.
Poseidon in wrath sent a sea-monster to devour the girl. When she was chained to the rocks, the hero Perseus spied her, slew the beast, and carried her off as his wife. The gods as a memorial, set the whole family amongst the stars as constellations.