Tilda Swinton on the White Witch

One of Tilda Swinton’s ancestors on her very posh, very military Scottish family tree was painted by John Singer Sargent, and it is easy to imagine Swinton, with her alabaster skin, otherworldly green eyes and regal 5-foot-11 bearing, captured in oils. “I do look like all those old paintings,” Swinton joked over a midsummer lunch of raw oysters at the Mercer hotel. “But I’m afraid my temperament does not conform. At all.”

She said this, as she said nearly everything, with a mix of direct authority and engaged enthusiasm that was both immediately ingratiating and commanding. Swinton, who is 44, was wearing no trace of makeup, a print sundress and flip-flops, and her hair, which is naturally red, was dyed white-blond. “I love the roots,” she said, as she tilted her scalp forward for inspection. “That’s the best part of being this blond.”

Her unique looks, her ease with herself and her voracious interest in the more esoteric worlds of cinema and style have made Swinton a kind of goddess of the avant-garde. In her movies, she has continually transformed herself — changing class, nationalities, gender. For “Orlando,” perhaps her most famous film, she played multiple incarnations of the title character, including a man. In “Thumbsucker,” opening in theaters on Sept. 16, she is utterly convincing as a suburban American mom. The director Jim Jarmusch cast her as an ex-girlfriend of Bill Murray’s in the recent “Broken Flowers,” in which she is terrifying, her face half-obscured by a foreboding curtain of long brown hair. For “The Chronicles of Narnia: The Lion, the Witch and the Wardrobe,” a big-budget movie that is due out from Disney at the end of the year, Swinton embodies the White Witch. “The studio couldn’t understand that someone evil would not have black hair,” she said. “They told me, ‘She has to be beautiful.’ I said: ‘The witch will be beautiful; the key is no makeup. After all, she’s the White Witch; her face should be bare.’ And I think, eventually, they saw my point. She’s very scary. I’m fully at peace with the idea that children who see this film will be backing away from me for the rest of my life.”