Canadian-American actor known for his roles in film, television, and theatrical production. He is best recognized for playing Questadt in The Godfather Part II and for playing William Mulder in The X-Files.
In 1950, he moved to the United States to study drama at Yale. His acting debut came in 1953 when he starred in the television production of The Clay of Kings. He went on to earn his first recurring television role in 1962 on the series Playdate.
He is known for having won the 1981 Drama Logue Award for Outstanding Performance for the play A Lesson from Aloes which he performed in Los Angeles, California.
He married Marijke DeJong in February of 1983. He is also the nephew of fellow actor Robert Donat.