The private side of 'The Duchess' ' Ralph Fiennes

RALPH FIENNES is not an easy man to get close to. Generally regarded as one of the finest actors of his generation, breathing the same rarefied air as the likes of Daniel Day-Lewis, he is similarly reluctant to engage in the cycle of personal revelation that usually accompanies publicizing a movie.

While promoting "The Duchess" at the Toronto International Film Festival this month, Fiennes recalled a lengthy interview with a writer for a glossy magazine who grew exasperated with his refusal to discuss his private sphere. "She got mad and said, 'You don't want to be known,' " Fiennes said, cutting a minimalist profile in a buzz cut and a trim black suit. "I don't want to be. I don't want to tell you everything, open up my heart. Why should I?"

Where audiences are involved, Fiennes is more comfortable playing a character than being himself. He recalled returning to the stage after a charity performance playing the garrulous Berowne in "Love's Labor's Lost" to ask for donations and suddenly being struck by stage fright. His voice jumped several octaves as he imitated his throat constricting in fear. "I'd been playing an extremely extroverted, high-energy character and I suddenly realized I had a whole other set of nerves that I got awkward about."

In "The Duchess," Fiennes plays William Cavendish, the duke of Devonshire, a brusque and often cruel man who relished the exercise of power but not the politicking that came with it. Where he is awkward and withdrawn, preferring the company of his dogs to that of other people, his wife, Georgiana (Keira Knightley), is a celebrated hostess and fashion plate, an English analogue to her friend Marie Antoinette. By way of synopsizing their relationship, biographer Amanda Foreman, on whose book the film is based, relates a moment when Georgiana flops playfully into her husband's lap and he, without apparent malice, drops her to the floor.

Georgiana, an indirect ancestor of Lady Diana, was the 18th century equivalent of a movie star, a beloved figure who drew crowds wherever she went. The duke, by contrast, is something of a cipher. "There aren't really records of his inner life, which is a blessing and a curse," said "The Duchess' " director and co-writer, Saul Dibb. "That means you've got very few clues to try and hold onto to get inside him, but it also gives you the possibility to imagine that inside this very repressed man is something more complex than a brute or a villain."