The cause was brain cancer, said his publicist, Kathie Berlin. Mr. Forster’s death coincided with the release of his latest film, “El Camino,” a spinoff of the AMC series “Breaking Bad,” in which he played a fixer who fashions a new identity for Bryan Cranston’s meth kingpin.

Mr. Forster began his film career as an Army private who, in “Reflections in a Golden Eye” (1967), gallops naked through the woods atop a black stallion, catching the eye of Brando and Elizabeth Taylor. More than four decades later, he found himself promoted to general, playing a military leader in “Olympus Has Fallen” (2013), an action thriller about a terrorist attack on the White House.

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In between came dozens of roles as cops, detectives and straight-talking heavies, in grindhouse pictures with names such as “Scanner Cop II: Volkin’s Revenge” and “Point of Seduction: Body Chemistry III.”

“My career went upwards for about five years and then downwards for about 27 years,” Mr. Forster told New York magazine in 2018, recalling his working life before “Jackie Brown” (1997), in which he played a melancholy bail bondsman named Max Cherry. The part was written for him by Tarantino, a former video-rental clerk who had admired Mr. Forster in movies such as “Medium Cool” (1969), a countercultural touchstone by filmmaker Haskell Wexler, and “The Delta Force” (1986), in which he played a Lebanese terrorist pursued by Chuck Norris and Lee Marvin.

Mr. Forster, who traced his ancestry to Italy, England and Ireland, was often cast against ethnic type, enlisted to play Native American figures or foreign despots such as Manuel Antonio Noriega of Panama and Moammar Gaddafi of Libya. Reviewing “Delta Force,” Roger Ebert wrote that he “gives a frighteningly good performance, intense and uncompromising,” and kept the film “from becoming just an action comic book.”

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In recent years, he worked with directors including Alexander Payne, as George Clooney’s father-in-law in “The Descendants” (2011), and David Lynch, as a detective in “Mulholland Drive” (2001) and as Sheriff Frank Truman in the 2017 Showtime revival of “Twin Peaks.” (Mr. Forster had previously been offered the part of Truman’s lawman brother, Harry, for the series’s original run in the early 1990s; he turned it down because he was working on another show, and the role went to Michael Ontkean.)

Mr. Forster’s late-career renaissance marked a return to the more artistically ambitious fare of his 1960s heyday, which began with “Golden Eye,” directed by John Huston and adapted from a novel by Carson McCullers. Mr. Forster had never made a movie — or ridden a horse — before the film, and told the pop culture website the A.V. Club that he was handed the equivalent of a tan jockstrap for his infamous equestrian nude scene.

He ultimately tossed the cloth covering into the bushes and recalled thinking: “ ‘Bob, if you are afraid to be naked on this horse, you’d better quit, because if you don’t do it with full abandon, with absolute abandon, then you have no right to be an actor. You’d better quit now.’ And that was the moment I said to myself, ‘All right, just go with it, Bob.’ ”

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Mr. Forster appeared alongside Peck in a western, “The Stalking Moon” (1968), and beginning in 1971 played the hard-boiled lead of “Banyon,” an NBC detective series set in 1930s Los Angeles. The show was canceled after about a dozen episodes, kicking off Mr. Forster’s self-described “27-year slump” — during which he starred in the short-lived police series “Nakia” and appeared in movies such as “The Black Hole” (1979), “Alligator” (1980) and “Vigilante” (1982).

As acting jobs dried up, he also found work as a drama teacher and motivational speaker, urging companies, organizations and (on at least one occasion) a group of imprisoned white-collar criminals to “deliver excellence right now” and “never quit.”

“No matter how bad things get,” he insisted, “you can still win it in the late innings.”

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That philosophy paid off for Mr. Forster when he was cast in “Jackie Brown,” based on Elmore Leonard’s novel “Rum Punch.” Tarantino had revived the career of John Travolta with his smash hit “Pulp Fiction” and, with “Jackie,” did the same for Mr. Forster and 1970s blaxploitation star Pam Grier, who played the title character, a money-smuggling flight attendant.

Mr. Forster received an Academy Award nomination for best supporting actor but lost to Robin Williams, for “Good Will Hunting.” Nonetheless, he said, “the nomination has given me my career back. And it’s created a tremendous amount of good will. . . . For a guy who could not get a job just a few years ago to now have people come up to me on the street and say nice things — it’s just astounding.”

Robert Wallace Foster Jr. was born in Rochester, N.Y., on July 13, 1941. (He later added an “r” to Foster after learning another actor shared his name.) His father was a Ringling Bros. elephant trainer who became an executive at a baking supply company; his mother was a homemaker.

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They divorced when Mr. Forster was 8, and his mother later killed herself after Mr. Forster received his draft notice in 1966. In part, he told the New York Times, “she was hysterical about the thought of my going to Vietnam.” Mr. Forster received a deferment, partly through medical statements describing the “devastating psychological effects” of his mother’s death.

Mr. Forster studied history and psychology at the University of Rochester, where he was mulling a career as a lawyer, when he spotted a young woman in a black leather raincoat. “As I was trying to think of what to say, I followed her into an auditorium,” he recalled in a Rochester alumni magazine interview.

Students were auditioning for a production of “Bye Bye Birdie”; the woman, June Provenzano, was a crew member. Mr. Forster landed a role in the chorus and fell in love with both acting and Provenzano, whom he married in 1966. They later divorced.

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After receiving a bachelor’s degree in 1964, Mr. Forster moved to New York, starring opposite Arlene Francis in a Broadway production of “Mrs. Dally Has a Lover,” which galvanized his acting career.

He later appeared in movies including “American Perfekt” (1997), a thriller by director Paul Chart, and “What They Had” (2018), in what Los Angeles Times critic Gary Goldstein described as “a stunning, Oscar-worthy turn as a man struggling to hold onto a blissful past to ward off a frightening future.”

His second marriage, to Zivia Forster, also ended in divorce. Survivors include his partner of 16 years, Denise Grayson; a son from a relationship, Bobby Foster; three daughters from his first marriage, Elizabeth Foster Howell, Maeghen Perry Dimperio and Kate Forster Simmons; and four grandchildren.

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In interviews, Mr. Forster rarely shied away from discussing the fallow period in the middle of his career and the toll it took on him and his family. “Every time it reached a lower level I thought I could tolerate, it dropped some more, and then some more,” he told the Chicago Tribune last year. “Near the end I had no agent, no manager, no lawyer, no nothing. I was taking whatever fell through the cracks.”

But “you know what,” he added, “everything teaches you something. The job of real life is the job of caring for others. Everything you do in life is superfluous compared to that.”