Robert Donner, a character actor who specialized in playing eccentrics, including the crazed prophet Exidor on the sitcom “Mork & Mindy,” died Thursday after suffering a heart attack. He was 75.

Donner appeared in more than 100 films and television shows, mainly as a character actor.

On “Mork & Mindy,” Donner led an invisible cult called the Friends of Venus on the ABC show that aired from 1978 to 1982. Whenever the friends only Exidor could see got in the way, he uttered his signature phrase – “Mork! Is that you?” – to series star Robin Williams.

“Bobby was very, very skilled at comedy. He worked all the time in an era when they were phasing out character actors,” said Michael Lembeck, whose father, Harvey, a comedic actor best known for his role on “The Phil Silvers Show,” taught Donner at comedy-improv workshops. “And he had a very droll, very dry sense of humor.”

That was evident in Donner’s official biography, which mentions he joined the Navy after high school, “serving three years, 11 months, 29 days, and six and one-half hours.”

Born April 27, 1931, in New York City, Donner grew up in New Jersey, Michigan and Texas. After experiencing the West Coast in the service, he decided to stay and attended what is now California State University, Northridge.

While living in a Los Angeles apartment, he became friends with a neighbor – Clint Eastwood. Mr. Eastwood thought Donner was funny and urged him to study acting, according to Donner’s biography.

With uncredited roles in two John Wayne Westerns – “Rio Bravo” (1959) and “The Man Who Shot Liberty Valance” (1962) – Donner started building a career.

He seemed to revel in “spooky, oddball roles of the street evangelist/undertaker/obsessive lawman variety,” according to the online database All Movie Guide.

Among Donner’s film credits are “Cool Hand Luke” (1967), “Vanishing Point” (1971),”High Plains Drifter” (1973), and “The Man Who Loved Cat Dancing” (1973). His final film, the family comedy “Hoot,” was released last month.

“I guess I’m like the rest of my fellow character actors,” Donner told the Arkansas Democrat-Gazette in 1988. “I keep my guns loaded and go where the action is.”

On television, Donner also had a long-running role as Yancy Tucker in “The Waltons” (CBS, 1972-81). He appeared in dozens of television series, including “Columbo,” “The Incredible Hulk,” “MacGyver,” “The Fall Guy,” “Matlock,” and “Falcon Crest.”

He was a founding member of Harvey Lembeck’s comedy-improv group, the Crazy Quilt Comedy Company, which included John Ritter, Penny Marshall and Williams.