Here is a comprehensive summary of the Wikipedia article on Mark Williams:

Mark Williams is an English actor, comedian, and screenwriter who first gained widespread recognition in the 1990s as a central performer in the BBC sketch show The Fast Show. Born in Bromsgrove, Worcestershire, and educated at Oxford University (graduating in 1978), he is perhaps best known to global audiences for his role as Arthur Weasley in seven of the Harry Potter films, starting with Harry Potter and the Chamber of Secrets in 2002, as well as for his roles in 101 Dalmatians (1996) and a 2012 appearance in Doctor Who as Brian Williams. Since 2013, he has starred as the title character in the long-running BBC drama Father Brown, and he also played the tipsy butler Beach in the 2013 adaptation of Blandings. Beyond acting, Williams has presented the daytime game show The Link (2014-2015) and several documentaries on industrial history, a personal passion, including Mark Williams' Big Bangs and Industrial Revelations.