According to Evelyn Christel, his secretary of 53 years, Robertson died of natural causes Saturday afternoon in Stony Brook, New York.
Born in Los Angeles in 1923, Robertson became famous with roles on TV dramas in the 1950s and early 60s, including 'Hallmark Hall of Fame,' 'Robert Montgomery Presents,' 'Wagon Train,' 'Playhouse 90,' 'Outlaws' and 'The Twilight Zone.'
He shot to movie stardom playing Lt. John F. Kennedy in the 1963 biographical war drama 'PT 109,' won an Oscar for 'Charly' in 1969, and went on to garner a new generation of fans with his appearance as kindly Uncle Ben in the 'Spider-Man' movies.
President John F. Kennedy himself reportedly had favored Robertson for the role in 'PT 109,' one that he remained proud of his whole life. However, Robertson had to change his hairstyle after Kennedy pointed out that his hair was parted on the wrong side.
Robertson carved out a TV career with a string of impressive performances, but he became almost equally well-known for missing out on playing the same roles when the TV dramas were made into movies. At various times he lost out to stars such as Paul Newman ('The Hustler'), Jack Lemmon ('Days of Wine and Roses') and Marlon Brando. He also memorably turned down major roles like 'Dirty Harry.'
Robertson won an Oscar playing a mentally disabled man in 'Charly,' a role he first made his own with the TV drama 'The Two Worlds of Charlie Gordon.' Both were based on Daniel Keyes' novel, 'Flowers for Algernon,' and Robertson said he'd been determined not to miss out on the big-screen version.
"I bought the movie rights to the show, and I tried for eight years to persuade a studio to make it," he said in 1968. "Finally I found a new company, ABC Films. I owned 50 percent of the gross, but I gave half of it to Ralph Nelson to direct." Later in life Robertson tried to make a sequel, going as far as to shoot 15 minutes of footage himself, but the project never got off the ground.
Robertson courted controversy in Hollywood and was effectively blacklisted for several years from the late 1970s after he blew the whistle on a senior studio executive who was embezzling money. "People told me I set a dangerous precedent," he said in 1994. "My ex-wife said that if I had played the game I would have owned the town, but I was always too independent."
Robertson continued to act on TV through the 1980s and '90s, landing roles on numerous TV movies and series like 'Falcon Crest.' He continued to act on TV right up until 2003, when he played Hal Molloy in political drama 'The Lyon's Den,' which starred Rob Lowe.
In a statement, Robertson's daughter Stephanie said "My father was a loving father, devoted friend, dedicated professional and honourable man. He stood by his family, friends, and colleagues through good times and bad. We will all miss him terribly."