Cliff Robertson, a ruggedly handsome actor who played the young John F. Kennedy as a wartime skipper in “P.T. 109” (1963) and who won an Oscar for his sympathetic portrayal of the mentally disabled title character in “Charly” (1968), died Saturday at a hospital in Stony Brook, N.Y. He had turned 88 on Friday.

His death was confirmed by the O’Connell Funeral Home in Southampton, N.Y., but no cause was provided.

In a career spanning six decades and more than 100 film and television credits, Mr. Robertson’s path to stardom was often thorny.

In the 1970s, he gained notoriety as a whistleblower in a check-forging scandal that fingered a studio chief as a thief and embezzler. He said that instead of being praised for his civic-mindedness, he was essentially blacklisted for several years for airing the indiscretion of a powerful mogul.

“The adage remains: ‘Thou shalt not confront big mogul on corruption, or thou shalt not work,’ ” Mr. Robertson said.

Mr. Robertson had long resented the Hollywood system that elevated him to stardom in “Picnic” (1955) with William Holden and “Autumn Leaves” (1956) with Joan Crawford, then seemed not to know what to do with him.

A versatile and subtle craftsman, Mr. Robertson bristled over the lack of quality control under a long-term studio contract.

He was cast as a pretty-boy hero in musicals, featherweight comedies and the most unlikely of dramas. He appeared as a beach-bum philosopher in “Gidget” (1959), opposite Sandra Dee, and as a Greek sponge diver in a trifle called “As the Sea Rages” (1960).

“Nobody ever did such a wide variety of mediocrity,” he told the New York Times years later.

While he held his own in virile parts — he was reportedly Kennedy’s personal choice for “P.T. 109” — Mr. Robertson was often at his best when he subverted his all-American good looks to play men of ruthless intelligence and sinister intentions.

As a right-wing presidential candidate in “The Best Man” (1964), based on a Gore Vidal play, Mr. Robertson was singled out by film critic Judith Crist for “dominating the screen with a ferocious and righteous passion.”

In “Three Days of the Condor” (1975), directed by Sydney Pollack, Mr. Robertson was a two-faced CIA officer who ordered a hit on an innocent researcher played by Robert Redford.

“Three Days of the Condor” was buoyed in popularity by its timeliness. It was made at the height of the political paranoia stemming from the Watergate scandal and congressional revelations of CIA misconduct. Film scholar Jeanine Basinger said Mr. Robertson “made a good villain for an era in which we were getting confused who were the good guys and who were the bad guys — because he looked like a good guy. There
was something quintessentially Ameri­can about him.”

By starring in “Charly,” playing a simple-minded bakery janitor who temporarily gains a genius IQ through a scientific experiment, Mr. Robertson made a bold move for a relatively big star, Basinger said. It would be decades before it became common for leading actors — including Sean Penn, Dustin Hoffman and Billy Bob Thornton — to play mentally disabled characters. The role earned Mr. Robertson an Academy Award.

Using his Oscar cachet, Mr. Robertson turned down big-budget roles he said were too politically extreme (“Dirty Harry”) or too violent (“Straw Dogs”) for his tastes.

In 1972, Mr. Robertson produced, directed, wrote and starred in “J.W. Coop.” He played an aging rodeo circuit performer who can’t adapt to the world after a stint in prison for writing bad checks.

The low-budget film drew strongly favorable reviews for its subtle balance of grit and pathos. Writing in The Washington Post, critic Tom Shales called it “a tour de force, but it’s more impressive just as an encouragingly good, genuinely unpretentious movie.”

The rest of Mr. Robertson’s career teetered in middling fare, but his financial independence kept him insulated from career pressures that have dogged some performers.

He carefully managed investments, and in addition was married from 1966 to 1988 to one of America’s richest women, the model and actress Dina Merrill, heiress to the E.F. Hutton and Post cereal fortunes. Her mother was the Washington hostess Marjorie Merriweather Post.

Mr. Robertson shunned Hollywood convention. He handled his own media relations and preferred living away from the film colony — at various times, he had homes on the beach near San Diego and the U.N. plaza in New York. He spent his free time flying his collection of small planes and participated in airborne famine-relief efforts in Nigeria and Ethiopia.

The only child of a prosperous rancher, Clifford Parker Robertson III was born Sept. 9, 1923, in La Jolla, Calif. He was a toddler when his parents divorced. His mother died, and he grew up with his maternal grandmother.

After service in the Merchant Marine during World War II, Mr. Robertson studied journalism at Antioch College in Ohio. His work on the college radio station led the dean to encourage him to pursue acting.

Playing a footless poet in “The Wisteria Trees” (1955) on Broadway brought him to attention of director Joshua Logan.

Logan cast Mr. Robertson in “Picnic,” a film adaptation of William Inge’s celebrated play set in a small Kansas town. Though a movie novice, Mr. Robertson showed great skill as the wealthy and volatile young man who loses beauty queen Kim Novak to a drifter played by William Holden.

The next year, Mr. Robertson was riveting as Joan Crawford’s emotionally unbalanced husband in “Autumn Leaves.” Crawford once called her co-star “stunning. Very few actors could have brought that kind of credibility to such a demanding part. His mad scenes can’t be topped.”

While acquiescing to studio demands in a run of undistinguished films, Mr. Robertson found more compelling work on live television. He played a pool shark in “The Hustler” and a married alcoholic in “Days of Wine and Roses.”

When it came time to cast the film versions, he was overlooked in favor of bigger stars: Paul Newman and Jack Lemmon, respectively. “I was starting to get a reputation as always a bridesmaid, never a bride,” Mr. Robertson said decades later.

He did, however, win an Emmy in 1966 for playing an obsessive gambler in “The Game,” directed by Pollack.

Mr. Robertson’s involvement with “Charly” dated to 1961, when he starred in a TV adaptation of Daniel Keyes’s story “Flowers for Algernon.” (Algernon is a lab mouse Charly befriends.)

Mr. Robertson bought the film rights to ensure he would get the starring role and said he spent seven years trying to generate studio interest.

Despite the Oscar triumph, the critical reaction was harsh. Mr. Robertson earned praise for his tender acting, but prominent reviewers found fault with a heavy-handed script and Ralph Nelson’s directorial tics: over-reliance on still shots, slow motion, split screens and multiple images.

Mr. Robertson’s first marriage, to Cynthia Stone, ended in divorce. His later marriage to Merrill also ended in divorce. Survivors include a daughter from the first marriage, Stephanie Saunders of Charleston, S.C.; a half-brother; and a granddaughter. A daughter from the actor’s second marriage, Heather, died.

The late 1970s saw a downward trajectory for Mr. Robertson’s career. He attributed the change to having pressed for an FBI investigation into a check-forgery scheme by Columbia Pictures boss David Begelman. Begelman had forged Mr. Robertson’s name on a $10,000 check, which the actor uncovered when he received a tax statement from the studio.

To Mr. Robertson’s dismay, many in the film community rallied around Begelman, a former agent who had recently guided financially ailing Columbia to profitability.

Begelman eventually pleaded no contest to the charges and was fined $5,000. He blamed the forgeries on a drug addiction. He continued to work for many years as a production chief, including a brief period as head of MGM. He killed himself in 1995, reportedly depressed by financial reversals.

After the Begelman affair, Mr. Robertson said he was consigned to a long run of supporting roles. He portrayed Playboy magazine founder Hugh Hefner in “Star 80” (1983), a film about slain playmate Dorothy Stratten, and was the kindly Uncle Ben to Tobey Ma­guire’s webby action hero in the “Spider-Man” series in the 2000s.

Uncle Ben died in the first “Spider-Man” film, but Mr. Robertson was asked to reprise the character anyway in the sequels.

“You talk about survival,” Mr. Robertson told the Los Angeles Times in 2006. “But director Sam Raimi said, ‘I want you back.’ . . . It’s wonderful to be wanted.”