Tyler was born Liv Rundgren at Mount Sinai Hospital in East Harlem, New York. She is the only daughter of Bebe Buell, a model, singer, and former Playboy Playmate (Miss November 1974), and Steven Tyler, the lead singer of Aerosmith. Her mother named her after Norwegian actress Liv Ullmann, after seeing Ullmann on the cover of the March 5, 1977 issue of TV Guide. She is of Italian, German, Polish, English and African American ancestry on her father's side and German ancestry on her mother's side.

In 2001, Tyler played the object of infatuation for three men (Matt Dillon, John Goodman, and Paul Reiser) in the comedy One Night at McCool's. In discussion of the role, she said it was "definitely the first part where I had to be so physically aware and have people so aware of me physically. Maybe it's not hard for anybody else, but it is a bit for me. I mean I love my body and I feel very comfortable in my skin but this was tough." Peter Travers of Rolling Stone wrote: "Tyler, a true beauty, gives the role a valiant try, but her range is too limited to play this amalgam of female perfection." In 2001, she starred in the feature film The Lord of the Rings: The Fellowship of the Ring, directed by Peter Jackson. She played the Elf maiden Arwen Undomiel. The film is based on the first volume of J. R. R. Tolkien's The Lord of the Rings. The filmmakers approached Tyler after seeing her performance in Plunkett & Macleane. She learned to speak the fictitious Elvish language that was created by Tolkien. Mick LaSalle of the San Francisco Chronicle noted that Tyler's performance was "lovely and earnest". A year later, Tyler again starred as Arwen in The Lord of the Rings: The Two Towers, the second installment of the series. The film received favorable reviews. She spent months learning sword fighting to be used during the concluding battle scenes in The Two Towers, but her scenes were removed after the script was changed. The film was an enormous box office success, earning over $926 million worldwide, out-grossing its predecessor, which earned over $871 million. In 2003, Tyler featured in the third and last installment of the series, The Lord of the Rings: The Return of the King. Following the success of The Lord of the Rings, she appeared opposite her Armageddon co-star Ben Affleck in writer-director Kevin Smith's romantic comedy Jersey Girl (2004), playing a woman who meets a widowed father played by Affleck, re-opening his heart to love. In an interview with MTV News, Tyler confessed that she felt "scared and vulnerable" while filming Jersey Girl, adding "I was so used to those other elements of the character [Arwen]. On The Lord of the Rings, a lot of things were done in post-production, whereas this was really just about me and Ben sitting there, just shooting off dialogue." However, she reiterated that doing Jersey Girl was what she wanted to do. In 2005, she appeared in Steve Buscemi's independent drama Lonesome Jim, where she was cast alongside Casey Affleck, as a single mother and nurse who reconnects with an old fling who has returned to their small town in Indiana after a failed run as a novelist in New York. The film was screened at a special presentation at the 2005 Sundance Film Festival where it was nominated for the Grand Jury Prize. Her next appearance in film was in a supporting role as an insightful therapist who tries to help a once-successful dentist (Adam Sandler) cope with the loss of his family in the September 11th attacks in Reign Over Me (2007).

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