At the height of the show’s popularity, Mr. Vaughn said he was receiving 70,000 fan letters a month.
The show was a self-aware parody of Ian Fleming’s creation James Bond, who had been played by Sean Connery in two hit movies by the time “The Man From U.N.C.L.E.” made its debut. (Fleming served as an adviser to the show, and is widely credited with coining the name Napoleon Solo.)
“The whole show is a joke. It’s an extension of the Bond joke into a gigantic cartoon in prime time,” Mr. Vaughn told The Saturday Evening Post in an 1965 interview, to which, the magazine noted, he arrived wearing a custom-tailored Italian suit and a black silk tie.
Joke or not, the show was wildly popular and catapulted Mr. Vaughn into overnight fame. It was also a platform for many other acting careers, most notably that of David McCallum, the Scottish actor who played Illya Kuryakin, the enigmatic Russian spy and Solo sidekick who developed a big fan following of his own.
Kurt Russell (at age 10), Leslie Nielsen and Joan Collins all appeared on the show. In the first season, William Shatner and Leonard Nimoy, who would co-star on “Star Trek” two years later, had roles in the same episode.
Despite his acclaim, Mr. Vaughn could be a little disdainful about his vocation. “Acting has always been very boring to me,” he told The Post. “Anyone not in television to become a millionaire is a simpleton.”
At the time, Mr. Vaughn was seemingly more focused on politics than show business: He often spoke publicly against the war in Vietnam.
“In our fervor to halt the potential spread of totalitarianism, what incredible precedent are we setting in Vietnam?” he asked in an impassioned speech. “By marching our legions through the countryside of foreign continents, burning homes, laying waste to the land and indiscriminately killing friend and foe alike?”
Mr. Vaughn became national chairman of an organization called Dissenting Democrats in 1967 and debated the war with William F. Buckley Jr. on Mr. Buckley’s television program, “Firing Line” — a bout that Newsday, on Long Island, said Mr. Vaughn had won. “Vaughn suffered no wounds from Buckley’s expert needling,” the newspaper said.
Mr. Vaughn befriended Attorney General Robert F. Kennedy and was a frequent guest at Hickory Hill, Kennedy’s estate in McLean, Va., where Mr. Vaughn played touch football with luminaries like the writer Art Buchwald and the astronaut John Glenn.
The Kennedys, Mr. Vaughn wrote in his name-dropping autobiography, “A Fortunate Life” (2008), were big fans. “The house was covered with U.N.C.L.E. posters inside and out,” he reported, “including pictures of me with my Walther P38 at the ready.”
Robert Francis Vaughn was born on Nov. 22, 1932, in New York City into a theatrically inclined household. His father, Gerald Walter Vaughn, was heard on radio series like “Gangbusters” and “Crime Doctor,” and his mother, the former Marcella Gaudel, appeared in a 1931 Broadway production of “Dracula.” The couple divorced when Mr. Vaughn was an infant and he moved with his mother to Minneapolis, where he was partly reared by grandparents.
“I was a complete wreck as a child, emotionally unstable, excessively prideful,” he told The Sunday News of New York in a 1965 interview.
When he was with his mother, she pushed his acting career, teaching him to recite the “To be or not to be” soliloquy from “Hamlet” when he was 5. While she was working as a cocktail waitress in a Chicago bar to earn extra money, his mother had young Robert perform the soliloquy for John Barrymore after Barrymore had dropped by. She later helped get her son cast on radio shows like “Let’s Pretend” and “Jack Armstrong, the All-American Boy.”
Mr. Vaughn headed to Hollywood in 1952. During the day, he studied theater arts at Los Angeles City College and played bit parts, including a Hebrew slave in the movie epic “The Ten Commandments.”
At night he would go to local hot spots and hobnob with other aspirants and the occasional star. He hung out with Johnny Carson, dated Natalie Wood and knocked back Cutty Sark at 2 a.m. with Bette Davis. He also befriended a young James Coburn and took credit for getting him a role in “The Magnificent Seven.”
After he graduated from college in 1956, Mr. Vaughn signed with Columbia Pictures for $15,000 a role. His career was temporarily waylaid when he was drafted; he served uneventfully as a drill sergeant in the Army and was discharged after 18 months.
After that, his life was a series of increasingly high-profile parts, and then he landed “U.N.C.L.E.” The show was such a success at first that he expected it to last for many years, but the ratings dropped, and it was canceled halfway through its fourth season.
He kept busy afterward, appearing on numerous TV shows and in movies like “Bullitt” (1968) and “The Towering Inferno” (1974). He also traveled extensively. He was in Prague in 1968 when Soviet tanks rolled into the city to suppress the local reform movement.
Mr. Vaughn earned a doctorate in communications from the University of Southern California in the mid-1960s. His dissertation, “The Influence of the House Committee on Un-American Activities on the American Theater 1938-58,” was published as a book, “Only Victims,” in 1972.
But the farther away he got from “U.N.C.L.E.,” the more Mr. Vaughn found himself taking roles that he characterized as “not quality,” among them a millionaire looking to dominate the world through computers in “Superman III” (1983) and a mercenary in “Battle Beyond the Stars” (1980), a low-budget science fiction epic conceived of as “The Magnificent Seven” in space.
In the late 1980s he acted as pitchman in an infomercial for the Helsinki Formula, which claimed to be a cure for baldness. The Federal Trade Commission eventually prevented the manufacturers from making this claim, but by then they had sold $100 million worth of the product.
In a 1993 interview with The Los Angeles Times, Mr. Vaughn was unapologetic about his work as a Helsinki Formula spokesman. “That was about the most profitable thing I’ve ever done in my life,” he said. “Every call that came in on the 800 number, I got a piece of that.”
During one of his rare returns to stage acting, he appeared in a production of “The Tender Trap” in Chicago in 1970. Also in the cast was the actress Linda Staab, whom he married in 1974 and who survives him. With his Hollywood stature on the decline, they moved to a castle-like stone home in Ridgefield, Conn., in 1981.
Mr. Vaughn’s survivors also include a daughter, Caitlin Vaughn; a son, Cassidy; and two grandchildren.
Mr. Vaughn continued to work as an actor into his 80s. In 2012 he appeared on two British television series, “Hustle” and “Coronation Street.” He was seen on an episode of “Law & Order: Special Victims Unit” last year.
Toward the end of his life, his view of acting, and of his luck in having a long show business career, grew rosier. As he put it in his autobiography, “With a modest amount of looks and talent, and more than a modicum of serendipity, I’ve managed to stretch my 15 minutes of fame into 50 years of good fortune.”