Conversation so far:
When did Robert Mitchum start acting?
Robert Mitchum starting acting in 1942
What was Robert Mitchum's first film?
His first foray into the genre film noir in the 1944 B-movie When Strangers Marry, about newlyweds and a New York City serial killer.

Question: Did he have a big role in that?
Self-contained rewrite: Did Robert Mitchum have a big role in that?