According to the Greek mythology, Cassiopeia was the wife of Cepheus, the king of Aethiopia, and they had a daughter, Andromeda. Cassiopeia always boasted about her daughter and her beauty saying they were more beautiful than the Nereids, the daughters of the sea god Nereus.  As a result, Poseidon became very angry and sent Cetus, the sea monster, to Aethiopia with the aim of destroying the country. After consulting a wise oracle, Cepheus and Cassiopeia decided to sacrifice Andromeda to calm Cetus.

They chained her to a rock next to the sea and left to be killed by the sea monster. Although she was about to die, Perseus managed to save her and kill the beast. Then, they got married.

Annoyed that Cassiopeia was not punished, Poseidon tied her to a chair in the heavens in a position that referenced Andromeda's ordeal. Cassiopeia is not always represented tied to a chair; in some drawings she is holding a mirror, symbol of her vanity, whereas in others she holds a palm frond.

   

     

This myth is the reason why Cassiopeia is located near to the pole star. In fact, the other characters of the myth (Andromeda, Cepheus and Perseus) are her neighbouring constellations.