Who is Cassiopeia from The Astonishing Life of Octavian Nothing, Traitor to the Nation, Vol. 1: The Pox Party and what is their importance?

Octavian's mother, Cassiopeia, is an African Princess. She is described as a beautiful woman, who is skilled in the arts of sketching and playing the harpischord. She is also said to be demanding. Cassiopeia hides her and her son's status as slaves from him for a time, claiming that she agreed to come to Lucidity College with Gitney when she was more than likely purchased.