Margaret Louise "Polly" Grubb (September 22, 1907 – November 17, 1963) was the first wife of pulp fiction author and Scientology founder L. Ron Hubbard, to whom she was married between 1933 and 1947. She was the mother of Hubbard's first son, L. Ron Hubbard, Jr. and his first daughter, Katherine May "Kay" Hubbard.