Gwendolen was a legendary queen of Britain, as told by Geoffrey of Monmouth in his pseudohistorical work Historia Regum Britanniae (History of the Kings of Britain; ). According to Geoffrey, she was the repudiated queen of King Locrinus until she defeated her husband in battle at the River Stour, the dividing line between Cornwall and Loegria, and took on the leadership of the Britons herself, becoming their first recorded queen regnant. Her victory and subsequent rise to fame as a righteous ruler shows how fractured Britain was at the time.