Mr. Robertson won an Oscar in 1969 for playing a mentally challenged bakery janitor in "Charly." After that he took roles in "Three Days of the Condor" and "J.W. Coop," which he also directed. But his ascent came to a halt in 1977, when he publicly accused Columbia Pictures president David Begelman of forging his name to a $10,000 studio check. Friends tried to persuade him to stay quiet, but Robertson spoke out. As a result, even though Begelman was found guilty, Mr. Robertson became persona non grata in Hollywood, finding little work until 1983. Clifford Parker Robertson III was born on Sept. 9, 1923, in San Diago. He became interested in acting in high school, and left Antioch College in Ohio to go to New York. Dark and handsome, he toured with the national company of Mister Roberts and made his Broadway debut in 1953 in Late Love. In 1955, he was in the cast of The Wisteria Trees, Joshua Logan's adaptation of The Cherry Orchard. The same year, he played a supporting role in the film adaptation of William Inge's Picnic, which was directed by Logan. On stage, he got his big break in 1957, when he was brought in to replace Robert Loggia in an out-of-town tryout of Orpheus Descending, Tennessee Williams' new play. He won a Theatre World Award for his performance.
From then on he devoted himself to film, making a sizable name for himself, but never quite achieving top-tier stardom. Among his standout roles were playing Lt. John F. Kennedy in "PT 109" (1963), Presidential candidate Joe Cantwell in "The Best Man" (1965), "Star 80" (1983), in which he played Hugh Hefner, and Ben Parker in "Spider-Man" (1992). The latter film, and its sequels, brought him some late-career attention. On television, in 1958, he portrayed Joe Clay in the first broadcast of "The Days of Wine and Roses." The role in the eventual film went to Jack Lemmon.
Mr. Robertson was married twice, to the actresses Cynthia Stone and Dina Merrill. Both marriages ended in divorce. He is survived by a daughter, Stephanie Saunders of Charleston, SC, and one grandchild. Another daughter, Heather Robertson, died in 2007.