His wife, Maria, told the New York Times the cause was complications of diabetes.
Donat, perhaps most recognizable for his recurring “X-Files” role, was also a frequent stage actor, playing Cyrano de Bergerac, Prospero, Shylock, King Lear and Hadrian VII over the years.
He also guest starred on TV series like “The F.B.I.,” “Hawaii Five-O,” “Mannix,” McMillan & Wife,” “Hill Street Blues” and “Murder, She Wrote.”
Francis Ford Coppola cast Donat as a lawyer in “The Godfather Part II” after he was considered for the role of Tom Hagen in “The Godather,” a part that eventually went to Robert Duvall. Donat also played Otto Kerner in Coppola’s “Tucker: The Man and His Dream” in 1980.
The Canadian-born actor originated from Kentville, Nova Scotia, and was drawn to acting by the career of his uncle, “Goodbye, Mr. Chips’” Robert Donat. His career began on stage, and he nabbed a few television roles before making his Broadway debut in 1957 in “The First Gentleman.”
In addition to his wife, Donat is survived by his sons, Caleb, Christopher and Lucas; two stepdaughters, Barbara Park Shapiro and Marina Park Sutton; a stepson, Malcolm Park; 11 grandchildren; and his brother, Richard, who is also an actor.