Matt Clark -- whose acting career spanned decades in film and TV working alongside some of Hollywood's biggest stars -- has died.

His family tells TMZ ... Clark -- arguably best known for his bartender role in "Back to the Future: Part III" and the TV sitcom "Grace Under Fire" -- died in his Austin, Texas home Sunday morning from complications after back surgery.

Clark appeared in several Westerns on the big and small screens alongside the likes of Clint Eastwood and John Wayne ... and he appeared in the '80s cult classic "The Adventures of Buckaroo Banzai Across the 8th Dimension."

He also appeared on the series "Grace Under Fire" ... along with classic shows including "Bonanza," Kung Fu," and "Dynasty."

His family tells us ... Clark was an "actor's actor" who loved and respected the job, but was not concerned with stars and fame. He was impressed when working with good people who loved their families. He felt "lucky" about his career ... and "he died the way he lived, on his terms."

He was 89.

RIP