Jean Rhys, 1966. Antoinette Cosway's life before becoming Mr Rochester's mad wife in Jane Eyre.
From Wikipedia
Wide Sargasso Sea is a 1966 postmodern novel by Dominican-British author Jean Rhys. Set in Jamaica in the 1830s–1840s, the novel is a postcolonial and feminist prequel to Charlotte Brontë's Jane Eyre (1847), detailing the background to Edward Rochester's marriage from the point of view of his wife Bertha Mason, Brontë's "madwoman in the attic", reimagined by Rhys as a Creole heiress named Antoinette Cosway.