Melissa Sue Anderson (born September 26, 1962) is an American-Canadian actress. She began her career as a child actress after appearing in several commercials in Los Angeles. Anderson is known for her role as Mary Ingalls on the NBC drama series Little House on the Prairie, on which she starred from 1974 until 1981. She is also known for her film roles, including Vivian in Midnight Offerings (1981), Ginny in the slasher film Happy Birthday to Me (1981), and Alex in the ABC Afterschool Special, Which Mother Is Mine? (1979) for which she won a Daytime Emmy.