Mærwynn was a 10th-century nun who served as the founding abbess of the reconsecrated Romsey Abbey. Appointed by King Edgar the Peaceable around 974, she acted as a foster mother to the king's daughter, Ælfflæd. While older legends incorrectly linked her to the era of Saint Patrick, historical records such as royal charters and the Liber Vitae of the New Minster confirm her role in English monastic life. She is recognized as a saint within both the Catholic and Eastern Orthodox traditions.