Of all the great Hollywood stars of the period between the wars, Marlene Dietrich was the most carefully manufactured, the most in control of herself. One doubts if she ever said an unconsidered word, just as she famously never allowed an image of herself, whether still or moving, to be used without careful vetting. Her sex life, which embraced both men and women, was famously varied, but despite the seemingly endless series of affairs, no hint of scandal was ever allowed to reach the general public. True, it was an age when such things were handled more discreetly by the media than they are now, but there was more to it than this. Dietrich never appears to have given herself to a grand passion or to have sought a relationship of permanence with any of her very many lovers, and consequently, though she was often openly homosexual she did not have to go through the disguises and repressions suffered by so many gay people in Hollywood.

Born in 1901 in Berlin to a police lieutenant and the daughter of a family of prosperous jewellers, her father died when she was six, leaving her to be brought up in an exclusively female world, though her mother remarried a man who was killed in the first World War. Marlene was a musically talented child, who learned the violin and soon graduated into the raffish, avant-garde and talent-filled world of Berlin theatre and cinema of the 1920s. She appeared in a series of forgettable and forgotten lightweight comedies and musicals, often in the chorus but gradually making her way up the ladder.

In 1928 her Svengali arrived in the person of the Viennese director Josef von Sternberg. Originally plain Joe Sternberg, the producers of one of his early films had tacked on the "von" to make him sound more aristocratic, "without my knowledge and without consulting me", according to himself. Von Sternberg made a series of highly regarded films, culminating in The Blue Angel, in which he put Dietrich in the leading role of the woman of easy virtue who is the subject of the obsession and ruin of a bourgeois school teacher.

Dietrich was unlikely casting, plump, not very good looking and with next to no experience in serious roles. But von Sternberg, a director who regarded actors as "marionettes, pieces of colour on my canvas" saw that, properly dressed and lit, she had a sensual magnetism that was made for the cinema.

The film was a huge hit and Dietrich quickly followed von Sternberg to Hollywood, from where he had already had offers. The rest is movie history. Dietrich went on to be one of the great stars, her face recognised all over the world, her husky voice parodied and imitated, at once a gay icon and a respected leader of her profession.

YET when one looks to see where exactly her talent lay, she remains curiously elusive. She was not a great actress in the conventional sense. Her performances were limited, her singing voice not of the first calibre and she didn't even appear in many good films. At the end of her life she regarded most of what she had done with contempt.

The secret of Dietrich's success appears to have lain in the fact that, in the words of the cliche, the camera loved her. Or rather, it was made to love her. Von Sternberg, for all his manipulation of her early career, also taught her everything he knew about the technique of making movies, particularly as they pertained to herself. In addition to lighting and costume, there was a meticulous attention to make-up, about which she was every bit as knowledgeable as the specialists who worked on her films.

On the set she knew what every one of the technicians was doing and why. Whether for movies or stills she always had a full-length mirror beside her within eyeshot, so that she could check how she looked. She always insisted on a key light about eight feet above her and a little to the right. This created hollows under the eyebrows and cheekbones that gave her a sculptured look. A cameraman recalled that she could simply lick her finger and hold it towards the key light, determining from the heat whether it was exactly the proper distance from her face.

Even at home, everything was arranged to show her off to her best advantage. A single pinpoint spot was focused above the fireplace and, eventually Dietrich would move into place, leaning against the mantlepiece so that her cheekbones were presented in all their glory to the visitors. It was narcissism developed into an art.

It all suited the high-gloss style of the Hollywood of her age to perfection. But even the most carefully preserved facade is eventually no defence against time. Prescient as always, Dietrich realised in the 1950s that her screen heyday was passing and returned to her beginnings as a cabaret artist. Her shows were, like everything else, carefully tailored, presenting an image of a glamorous, tough and slightly decadent lady, but not so much so as to alienate middle-class audiences.

Enigmatic to the last, she retired in the 1970s and spent almost 20 of the last years of her life as a recluse in a Parisian apartment, determined, it seems, that the ravages of age would never dispel the careful image of her films.

Marlene Dietrich: a Legend, a series of four Dietrich films, will be screened during the festival: Marlene, Sunday, April 9th, IFC 2, 6.45 p.m; The Blue Angel, Monday, April 10th, UGC 6, 5 p.m.; Rancho Notorious, Tuesday, April 11th, UGC 6, 2.15 p.m.; Touch of Evil, Wednesday, April 12th, UGC 6. 2.30 p.m.

An exhibition of photographs of Marlene Dietrich, A Legend in Pictures, will run at the Gallery of Photography from April 6th- 29th

Fergus Linehan is a novelist, playwright and former Arts Editor of the Irish Times