Peter Donat died on Monday at the age of 90 at his home in Point Reyes Station, California.
X-Files fans will recognize Donat from his run as Fox Mulder's father William Mulder, appearing in six episodes of the show total.
Born Pierre Collingwood Donat on January 20, 1928, in Kentville, Nova Scotia, Donat held Hawaii Five-O, Dallas, Murder, She Wrote, The Outer Limits, and Hill Street Blues among his list of guest-starring TV roles.
X-Files Co-star David Duchovny share this tribute to his on-screen father: "Peter had an easy gravitas as a performer and seemed to come from that generation that took the art seriously but not too seriously".
While he had steady work as a television and movie actor, he always preferred the stage to either, performing with production companies like the American Conservatory Theater and the Stratford Festival, where he played roles like Bergerac, King Lear, and Hadrian VII.
Pierre Collingwood Donat was born on January 20, 1928, in Kentville, Nova Scotia.
Peter was married to actress Michael Learned from 1956 until 1972, when they divorced. Donat was once considered for the role of Tom Hagen in The Godfather, but it ultimately went to Robert Duvall. He also appeared in the Francis Ford Coppola films "The Godfather Part II" and "Tucker: The Man and His Dream".
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.