Mark Williams is an English actor, comedian, presenter and screenwriter. He first achieved widespread recognition as one of the central performers in the popular BBC sketch show The Fast Show. His film roles include Horace in 101 Dalmatians (1996) and Arthur Weasley in seven of the Harry Potter films. He made recurring appearances as Brian Williams in the BBC television series Doctor Who and as Olaf Petersen in Red Dwarf. Since 2013, Williams has portrayed the title character in the long-running BBC series loosely based on the Father Brown short stories by G. K. Chesterton.

The Fast Show, known as Brilliant in the US, is a BBC comedy sketch show that ran from 1994 to 1997, with specials in 2000 and 2014. The show's central performers were Paul Whitehouse, Charlie Higson, Simon Day, Mark Williams, John Thomson, Arabella Weir and Caroline Aherne. Other significant cast members included Felix Dexter, Paul Shearer, Rhys Thomas, Jeff Harding, Maria McErlane, Eryl Maynard, Colin McFarlane and Donna Ewin.