He performed many stage, television, radio and film roles, and was recognised for having a "rich, sonorous voice" and often playing villains and officers.

His guest roles included multiple appearances in the cult series The Avengers (1962–68) and Doctor Who (1968–69, 1976, 1978–79), as well as playing the U-boat captain in the Dad's Army episode "The Deadly Attachment" (1973).

Madoc was born near Merthyr Tydfil and attended Cyfarthfa Castle Grammar School, where he was a member of the cricket and rugby teams,[4] and displayed talent as a linguist.

He eventually spoke seven languages, including Russian and Swedish, and had a working knowledge of Huron Indian, Hindi and Mandarin.

According to The Daily Telegraph, BBC News and The Times,[7][6][8] Madoc is especially remembered for his role in "The Deadly Attachment", an episode of the comedy Dad's Army in which he played a U-boat captain held prisoner by the Walmington-on-Sea platoon of the Home Guard.

Madoc also played a German villain in the TV series Fortunes of War, directed by James Cellan Jones.

He also appeared in five episodes of the TV series The Avengers between 1963 and 1969 ("The Decapod", "Six Hands Across a Table", "Death of a Batman", "The Correct Way to Kill", "My Wildest Dream").

(1967), Doppelgänger (1969), Hell Boats (1970), Dr. Jekyll and Sister Hyde (1971), Soft Beds, Hard Battles (1974) and Operation Daybreak (1975).

He acted a small role in the second Peter Cushing film, Daleks' Invasion Earth 2150 A.D. (1966), and was later cast in the television series itself four times.

He appeared twice in the drama series UFO, once as the partner of Ed Straker's estranged wife (in A question of priorities) and once as the captain of a British warship under attack by the aliens (in Destruction).

He also starred as Ellis Peters's medieval detective Brother Cadfael in the BBC Radio 4 adaptations of Monk's Hood,[9] The Virgin in the Ice[10] and Dead Man's Ransom.

[citation needed] The Welsh actor voiced Gwydion in Y Mabinogi (Otherworld) (2003), featuring Daniel Evans, Jenny Livsey and Matthew Rhys.