Mary Katherine "Merricat" Blackwood is a fictional character from the novel *We Have Always Lived in the Castle* by Shirley Jackson. She is a young woman living with her older sister, Constance Blackwood, and their ailing uncle in a secluded mansion. The family is ostracized by the local community due to a tragic incident that occurred years earlier. Merricat is known for her eccentric behavior and strong attachment to rituals, which she believes protect her and her family. She often engages in magical thinking and has a deep connection to the surrounding nature, reflecting her desire for control in a chaotic world.