​From Wikipedia, the free encyclopedia.   Stephen Mangan (born 22 July 1972) is an English actor, best known for his roles as Guy Secretan in the television series Green Wing, Dan Moody in I'm Alan Partridge and as Holistic Detective Dirk Gently in the 2010 BBC adaptation of Douglas Adams' book Dirk Gently's Holistic Detective Agency. Description above from the Wikipedia article Stephen Mangan , licensed under CC-BY-SA, full list of contributors on Wikipedia.