Fiona Mary Shaw, CBE (born Fiona Wilson; 10 July 1958) is an Irish actress and theatre and opera director, known for her role as Petunia Dursley in the Harry Potter films and her role as Marnie Stonebrook in season four of the HBO series True Blood (2011). She has worked extensively with the Royal Shakespeare Company and the National Theatre, twice winning the Olivier Award for Best Actress; for various roles including Electra in 1990, and for Machinal in 1994.