Peter Donat -- who appeared on several popular TV shows during his 50-year career and played Mulder's father on "The X-Files" -- has died ... according to his wife.
He reportedly died Monday at his home in Point Reyes Station, California from complications of diabetes.
Donat began his career in 1953 and was a familiar face on television for decades. He guest-starred and had recurring roles on shows like "Mission: Impossible," "The F.B.I.," "The Waltons," "Hawaii Five-O," "Hill Street Blues" and "Murder, She Wrote."
Peter had a notable role in the famous "Who Shot J.R.?" episode of "Dallas" in 1980 ... and played William Mulder, Agent Mulder's dad, on 6 episodes of "The X-Files." His film credits include "The Godfather Part II," "The War of the Roses" and "The Game."
The veteran actor had a long career on Broadway as well, making his debut in 1957.
He was 90.