The first American gamine, the Iowa-born Jean Seberg became an icon in French and American cinema during the 50s and 60s. With her pixie-cut hair, elfin features, and breathy voice, she was our answer to Audrey Hepburn and Leslie Caron. She was discovered by Otto Preminger, who would direct her in two films. She made her film debut as Joan of Arc in 1957's "Saint Joan," a role she beat out 18,000 other actresses for. She was only 17 years old.
Her next film, "Bonjour Tristesse," put her alongside such greats as David Niven and Deborah Kerr. This is personally one of my favorites of Seberg's films. The film tells the story of a French teen's guilt resulting from a summer spent with her father, his mistress, and another woman on the Riviera. One of the most interesting things about this film is that it is made half in color, half in black-and-white in order to illustrate the happy times and the unhappy times in the girl's life.
Seberg then became the poster girl for French New Wave cinema when she was cast in Jean-Luc Godard's "À Bout de Souffle" (another of my favorite films of her's). The image of Seberg in black cigarette pants and a Herald Tribune sweater while walking the streets of Paris with Jean-Paul Belmundo has become iconic. Seberg also starred in the Warren Beatty vehicle "Lilith," "In the French Style," "The Beautiful Swindlers," "A Fine Madness," and the 1970 disaster film "Airport," among many others.
As the sixties progressed, Seberg used her celebrity status to advocate her beliefs. She supported to NAACP, Native American Rights, and the controversial Black Panther Party. Because of her international influence, Director of FBI J. Edgar Hoover considered this actress a threat to national security and launched a secret capaign for Seberg to be "neutralised." The FBI kept close tabs on her, tapping her phone lines. In 1970, when Seberg became pregnant by her second husband Romain Gary, the FBI saw an opportunity to completely discredit the leftist Seberg. They "leaked" a story to gossip columnists at the LA Times and Newsweek that the child wasn't fathered by Gary, but by a Black Panther Party member. The story caused so much stress for the seven months pregnant star (who already was prone to anxiety and depression) that it brought on premature labor. She gave birth to a baby girl, but the infant died two days later in the hospital. The day after the child's death, Seberg called a press conference in hopes of putting rumors to rest, and she presented the reporters with the body of her death white child as proof. Though effectively putting an end to rumors of her romantic involvement with a Black Panther, Seberg could not escape being hounded by the FBI.
At this point, friends of Seberg said she became withdrawn and suicidal following the death of her child, becoming increasingly dependent on alcohol and prescription drugs in order to even function. She relocated to Paris in order to escape the FBI, but that didn't improve her fragile state. Despite producing a son, her marriage to Gary fell apart, and Seberg would go through two more husbands before the decade's end. During the seventies, she made numerous suicide attempts ranging from overdoses to trying to throw herself in front of a Paris Metro train. Every year on the anniversary of her child's death, she attempted suicide.
In early 1979, Seberg married Algerian "playboy" Ahmed Hasni and moved with him to Barcelona, only to flee back to Paris a few weeks later in order to escape Hasni's abusive nature. At this point, despite promise that she was going back to make films and would turn her life around, Seberg felt she was completely alone. In August 1979, Seberg went missing for 11 days until she was found dead in the backseat of her car in Paris after almost two weeks. She had taken a massive overdose of barbituates and alcohol, and left a note saying, "Forgive me, I can no longer live with my nerves." She was only 40 years old. Her second husband, Romain Gary, committed suicide a year after her death. Her funeral was attended by Jean-Paul Satre, Simone de Bouvoire, and several directors and actors who worked with this incredible talent.
Rumors arose as to whether or not the FBI had been involved in her death. There were no pill or alcohol bottles in any proximity of Seberg, and yet the alcohol level was far too high far Seberg to have driven to a secluded place to kill herself. Also, Seberg needed glasses in order to drive and never left without them, but her glasses weren't in her car upon her death. But, given her depressive and suicidal nature, these rumors were overlooked and her death was ruled a suicide.
The cultural legacy of Jean Seberg can be seen even though she passed away almost thirty years ago. She is still very popular and celebrated in France, her gravesite in Montparnasse a pilgrimage for many. Kirsten Dunst cropped her hair off a years ago in order to propose a biopic starring herself as Seberg. Several films, plays, books, musicals, photoshoots have been inspired by Seberg's body of work and sense of style. Her smart beatnik style consisting of black cigarette pants, black ballet flats, and a striped boatneck shirt has long influenced Parisian fashionistas.

Further reading:

"The FBI vs. Jean Seberg"
http://www.time.com/time/magazine/article/0,9171,947393,00.html

"Saint Joan" fanpage (including an interview between Seberg and husband at the time, Romain Gary)
http://www.saintjean.co.uk/menu2.htm

Another good Jean Seberg page
http://www.tedstrong.com/jeanseberg.html