Who is Roxana from Pudd'nhead Wilson and what is their importance?

Roxana is a slave, but as she is only one eighth black, she appears to be white. Roxana is a slave in the household of Percy Driscoll, who fathers her child. Ironically, Roxana and her mistress give birth the same day, and Roxana takes over the care of her mistress' son because she dies a few days later. Everyone comments on the boys similarities, and one night, Roxana becomes frightened that her child will be sold down river. She considers killing the baby and herself, before realizing that she can exchange her own baby for the Driscoll baby. In doing so, her son can live to be a gentleman and never fear being sold down river.