Mark Williams (born 22 August 1959) is an English actor, screenwriter and presenter. He is best known as Arthur Weasley in the Harry Potter films, and as one of the stars of the popular BBC sketch show The Fast Show. He also played Brian Williams in the BBC series Doctor Who, and Olaf Petersen in Red Dwarf. More recently he has appeared as the title character in the BBC series Father Brown.
Williams was educated at North Bromsgrove High School and Brasenose College, Oxford. He performed with Oxford University Dramatic Society (OUDS). Having made a career as a theatre actor and working for the Royal Shakespeare Company and the Royal National Theatre along the way, he came to wider public attention through his appearances on the BBC television sketch programmes Alexei Sayle's Stuff and The Fast Show. Williams has described the huge popularity of the latter show as a "double-edged sword" as it has led to his being seen by the public as a comedian rather than as an actor.