Sister Aloysius is a fictional character from the play and film titled Doubt: A Parable, created by John Patrick Shanley. She serves as the strict principal of a Catholic school in the 1960s and is known for her strong moral convictions and unwavering authority. Sister Aloysius is deeply concerned about the well-being of her students and is particularly vigilant regarding the behavior of the school's priest, Father Flynn. Throughout the story, Sister Aloysius becomes suspicious of Father Flynn's relationship with a student, leading her to confront him about her concerns. Her character embodies themes of doubt, certainty, and the complexities of faith, making her a central figure in the narrative's exploration of moral ambiguity.