David H. M. Hemblen was an English-born actor, who frequently worked in Canadian film, television, and theatre and grew up in Toronto, Ontario.
He pursued a classical education before turning to theatre. He received an M.A. in English and was working towards a Ph.D. in Medieval Studies when he was spotted during a rehearsal of a university production by Clifford Williams of the Royal Shakespeare Company. He was offered a season at Toronto's Royal Alexandra Theatre. He began his career in theatre in the 1960s. His stage career includes more than 70 productions as actor/director at major Canadian theatres, including the Stratford Festival and four seasons at the renowned Shaw Festival in Niagara-on-the-Lake. For his portrayal of Dr. Astrov in Toronto's Tarragon Theater production of Uncle Vanya, he received a Dora nomination for Best Leading Actor. He was a mainstay on the television series Earth: Final Conflict, playing Jonathan Doors, a role he is best known for. He appeared in the first two seasons as a main character and remained in the third season as a recurring character until being killed off in season four.