Bertolucci began writing at the age of fifteen, and soon after received several prestigious literary prizes including the Premio Viareggio for his first book. His father's background helped his career: the elder Bertolucci had helped the Italian filmmaker Pier Paolo Pasolini publish his first novel, and Pasolini reciprocated by hiring Bernardo as first assistant in Rome on Accattone (1961). But Bertolucci's potential had already been noticed by others, such as Sergio Leone, who asked him to write the storyline for Once Upon a Time in the West. Leone later rejected it as too cerebral for an American audience.

In 1962, at the age of 21, he directed his first feature film, La commare secca (1962) The film is a short murder mystery, following a prostitute's homicide. Bertolucci uses flashbacks to piece together the crime and the person who committed it. The film which shortly followed was his acclaimed Prima della rivoluzione (Before the Revolution, 1964).

The boom of Italian cinema that gave Bertolucci his start slowed in the 1970s, as directors were forced to co-produce their films with several of the American, Swedish, French, and German companies and actors due to the effects of the global economic recession on the Italian film industry. It has been speculated that this is the point in its history at which Italian cinema began to depend upon the international market.

Directors increasingly were forced to co-produce their films with French, American, Swedish, and German companies, in order both to finance them and to appear competitive in the now-international entertainment industry. Bertolucci was no exception. Last Tango in Paris (1972), starring Marlon Brando and Maria Schneider exemplified the new trend for Italian movies to make more money by employing foreign actors in starring roles: Last Tango included only one Italian actor, Massimo Girotti, in a main role. Bertolucci's 1900 (1976), starring Burt Lancaster, Donald Sutherland, Robert de Niro, and Gerard Depardieu, is often said to mark the point at which the Italian film industry's dependence on the international market began to contribute to the disintegration of its national identity, although the film itself is entirely focused on an Italian theme: it chronicles the lives of two men during the political turmoils that took place in Italy in the first half on the 20th century.

Bertolucci might not regret this disintegration: he is actively political, and a confessed Marxist. Like Visconti, who similarly employed many foreign artists during the late 1960s, Bertolucci uses his films to express his own political views; hence they are often autobiographical as well as highly controversial. His political films were preceded by others re-evaluating history. The Conformist (1970) criticised Fascist ideology, touched upon the relationship between nationhood and nationalism, as well as issues of popular taste and collective memory, all amid an international plot by Mussolini to assassinate a professor of politics in Paris, France. 1900 also analyses the struggle of Left and Right. The 1987 epic The Last Emperor (recently re-released at an extended 219 minutes) allowed Bertolucci to influence politics both through his characters and through the act of making the film itself. He was granted unprecedented permission to film in the Forbidden City of Beijing, and the film's central character Pu Yi undergoes a decade-long communist re-education under Mao which takes him from the peacock colours of the palace to the grey suit worn by his contemporaries to live out his life as a gardener.

Many critics consider sex and politics the defining characteristics of Bertolucci's films. Last Tango examines sex in an extremely carnal and disturbed way. It is seen as an erotic film which opened the door to eroticism in general-release films. The Conformist is based political themes, more specifically, fascism, and the relationship between personal comfort and ideals. The film deals with Fascist Italy and can be seen as both artistic and intellectual. This film is thought to demonstrate his excellence as a director. While he has directed, written, or been otherwise involved in dozens of movies over five decades, and his range is extremely broad, these themes nonetheless figure prominently throughout his work, especially in his most noted and most recent releases. Stealing Beauty offers little heterogeneity and The Dreamers manages to include both subject matters and little else. Whether this narrowness is Bertolucci's intent merely a symptom of the narrowness some critics accuse him of, he has used the controversy aroused by his films iconoclastically to encourage people to reconsider themselves and their society; he is often considered successful in pushing back the boundaries of propriety. Bertolucci enthusiasts will also notice the similarites between characters in films, particularly in the two most recent (Stealing Beauty, 1996, and The Dreamers, 2003). For example, the two female leads in both films (Liv Tyler and Eva Green), are fair of skin, slender, dark haired and blue eyed. Both characters are heavy smokers during the fashionable ages of youth, and both are shown losing their virginities, at the age of nineteen. In both films, Bertolucci speaks of 'proof of love,' using almost the exact same lines each time.

In The Dreamers, the character Isabelle, declares she was born in 1959 even though the film is set in the late sixties. This line is not to be taken literally; it is a reference to Jean-Luc Godard's film Breathless (1959) as the character then proceeds to renact a famous scene from the Godard film.

Bertolucci also has a talent for putting the human soul under the microscope. Psychoanalysis is as central to his films as it is to Woody Allen's, and Marlon Brando claimed that Bertolucci's sharing of psychoanalytical confidences with the star on the set of Last Tango in Paris helped elicit the performance that many consider Brando's best. Bertolucci himself is also known for the number of psychologists who have followed him everywhere, even interpreting his dreams, as a subject of dissertations and research on the creative artist. His interest in understanding the human condition has led to the many explicit scenes in his films.

Last Tango in Paris presents Marlon Brando's character Paul as he finds comfort in an anonymous affair after the death of his wife in violent circumstances. The film caused controversy in Italy for a sodomy scene, and it was sequestered by the censorship commission and all copies were ordered destroyed. An Italian court revoked Bertolucci's civil rights for five years and gave him a four-month suspended prison sentence. Many years after, when the general modesty had changed and the censorship commission had been abolished, the film reappeared and was projected in a slightly censored version.

In this and other films, Bertolucci examines the power of sexual relations in people's lives. Stealing Beauty gives a visual account of a girl growing into a woman during a summer abroad. His latest work, The Dreamers, has been criticised not only for its extensive sex scenes but also the inclusion of male masturbation. In it, the sexual relations of three main characters serve to expose their thoughts. For instance, when Theo is shown to masturbate it is in the context that the one he loves the most, his sister, seems to be growing away from him and he can see the development of a relationship between the newcomer and his sister that excludes him.

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