Qualified as an MD
He made four films with Patrick Troughton: Hamlet (1948), Chance of a Lifetime (1950), Jason and the Argonauts (1963) and The Viking Queen (1967).
Towards the end of his life, he returned to his original profession of medicine and was working as a locum in South Wales at the time of his death from cancer.
Appeared in five Best Picture Oscar nominees: 49th Parallel (1941), Henry V (1944), Hamlet (1948), The Nun's Story (1959) and Becket (1964), with Hamlet winning Best Picture.
Niall was a presence in countless medieval films in the 40s, 50s, and 60s. A lot of films with ancient settings too.