The Scottish-born Mr. Williamson was perhaps best known for his acclaimed portrayal of the wizard Merlin in the 1981 film Excalibur and for his turn as the drug-addicted yet brilliant Sherlock Holmes in the 1976 movie The Seven Per-Cent Solution.
Mr. Williamson, who lived in Amsterdam, died Dec. 16 at 75 after a two-year struggle with esophageal cancer, said his son, Luke.
He announced the death Wednesday on his father's website.
Upon seeing Mr. Williamson portray Hamlet in London in 1969, the New York Times review declared that the title of "Greatest English Actor of his Generation" was about to fall on Mr. Williamson's shoulders.
He appeared to be drawn to roles that presented "a marathon challenge to his ability to portray the darker human emotions," the Los Angeles Times said in 1969, while noting that he was "touchy, mercurial - and very, very talented."
Since the early 1960s, Mr. Williamson had regularly acted in films but often gave well-reviewed performances in lesser-seen movies, a list that included The Seven-Per-Cent Solution and Robin and Marian (1976), in which he played a subdued Little John to Sean Connery's Robin.
His stage and screen career stretched into the late 1990s and included the one-man Broadway show Jack: A Night on the Town With John Barrymore.
While trying to assess what happened to "a superstar - the Hamlet of his generation," the London Independent said in 1993 that "the reasons given for his absence" from the London stage "are many. They include tax and booze and the breakup of his marriage to actress Jill Townsend."
Yet as early as 1971, Mr. Williamson had announced that he was no longer interested in being "the greatest actor of my generation, and all that jazz," and that same year he released an album of country music in Britain.
About two decades ago, he retreated to Amsterdam and, increasingly, his music. Before he died, he was able to finish recording the CD he had been working on, said his son, Mr. Williamson's only immediate survivor.
