Mariclare Catherine Costello (February 3, 1936 – April 17, 2026) was an American actress. She was a lifetime member of The Actors Studio. Costello's most notable role was that of Rosemary Hunter Fordwick on the television series The Waltons, from 1972 to 1977. In 1977, after her role on The Waltons, she played matriarch Maggie Fitzpatrick on the short-lived drama show The Fitzpatricks.