After months of speculation, American actress Rooney Mara has been chosen to play spiky-haired bisexual hacker Lisbeth Salander in the Hollywood adaptation of Stieg Larsson's Millennium Trilogy, under director David Fincher. The selection of the little-known Mara brings to an end "one of the most drawn out and closely watched casting searches for an actress in years," writes Mike Fleming at Deadline Hollywood. Here's a quick guide to the world's newest movie star:

Where might I have seen Rooney Mara before?
The 25-year-old appeared briefly in Michael Cera vehicle Youth in Revolt, and played the lead role of Nancy in the recent remake of A Nightmare On Elm Street. She will be seen in upcoming release of Fincher's The Social Network (a.k.a the Facebook movie). (Watch a slideshow of Rooney Mara images)

Anything else I should know about her?
Her sister Kate is also an actress, and appeared as Heath Ledger's daughter in Brokeback Mountain. She has a family background in the world of football: One great-great-grandfather, Wellington Mara, founded the New York Giants, and another, Art Rooney, founded the Pittsburgh Steelers.

Who else was up for the role?
Almost every twenty-something actress in Hollywood. Other big names in the frame included Natalie Portman, Ellen Page, Scarlett Johansson, and  Emma Watson, whose recent elfin haircut was was seen by commentators as an indicator of her high level of interest in the role.

What do film critics think of the decision?
Fincher is "no stranger to mining new talent," says Steven Zeitchik in the L.A. Times. Don't forget he gave Twilight star Kristen Stewart her big break in Panic Room. Mara displayed a "quiet confidence" playing a similar "strong but lonerish type" in A Nightmare on Elm Street. "She'll probably do just fine." I'm not so sure, says Julie Steinberg at the Wall Street Journal. "It takes a certain fierceness to play a tattooed, socially-challenged, combative hacker." At first glimpse, Mara looks too "gentle." But give her a few "piercings and protein shakes," and we shall see. 

When will the movie be released?
Not until December 21, 2011. Filming begins in Sweden in the fall, with Daniel Craig playing investigative journalist Mikael Blomkvist, Robin Wright as his occasional lover Erika Berger, and Stellan Skarsgard as industrialist Martin Vanger.

Sources: Deadline Hollywood, L.A. Times, Wall Street Journal, iMDB