“She’s one of those characters, like Jesus Christ, Dracula and Batman, that everyone has his own ideas about who should play them,” Mr. Fincher said, treating himself to a single martini and a meal that consisted mostly of salad. “All of a sudden I’m getting phone calls from people I respect saying, ‘You can’t possibly cast X, Y or Z.’

“I wanted to say, ‘Are you really calling me to influence the casting of a movie?’ I was naïve about it, to be honest. It wasn’t like there were 5,000 girls in black leggings and goth skull makeup lining up outside on the street. But a lot of the press and the bloggers made it seem like the search for the next Scarlett O’Hara.”

In the end Mr. Fincher picked 26-year-old Rooney Mara. As her name suggests, Ms. Mara is a descendant of two great N.F.L. dynasties, the families that own the Steelers and the Giants, but except to fans of the “Nightmare on Elm Street” franchise (she was Nancy in the 2010 remake) and to viewers who paid attention at the very beginning of Mr. Fincher’s “Social Network,” in which she appeared briefly but memorably as Mark Zuckerberg’s girlfriend, she is an unknown to most moviegoers. To Mr. Fincher that was part of her appeal.

The Salander character, he explained, never answers questions about herself, and at the beginning no one knows anything about her. “Lisbeth is not a Hot Topic goth,” he said. “She’s not Joan Jett. She’s somebody with a safety pin in her cheek. It’s original punk. She has created a way to be seen as trash. Part of that is a stay-away thing, and part of it is a self-conscious agreement with what everyone thinks of her. She thinks, ‘I’ll live with that if it means no one ever takes advantage of me.’ ”