Joseph Goebbels may have been a genius of spin; Albert Speer may have designed the buildings.

But it was Leni Riefenstahl who provided the choreography and gave the Nazi movement the visual impact recently admired by Bryan Ferry.

Triumph Of The Will is quite simply the greatest propaganda film ever made. It's a judgement that in no way valorises the content nor exculpates a woman who only died in 2003, aged 101, still unrepentant.

Her usual tack, when faced with difficult questions, was either denial or amnesia, whether about the Konskie massacre of September 1939 or, more innocently, her nude appearance in an early Health & Efficiency-style film called Way s To Strength And Beauty.

I met Riefenstahl three times between 1978 and 1984 and was struck by the disparity between her apparent forgetfulness about the war years and her ability to remember every camera angle, emulsion, exposure and edit in all of her films.

She was certainly present at Konskie and may even have intervened in an attempt to prevent the killing of Polish civilians implicated in the death of five German soldiers. There is a photo of her looking frightened and upset as the shooting begins.

In later years, however, she denied all knowledge of the event.

Her reticence about Ways To Strength And Beauty is harder to understand. She certainly wouldn't have been embarrassed about appearing nude. Undraped figures, admittedly lent propriety by allusion to classical Greece, were a stock element of Olympia, her first masterpiece, which was intended as PR underpinning for Hitler's triumphant Berlin games of 1936;

in the event, all that good work was undone when Jesse Owens ran off with the medals.

Riefenstahl began her career as an expressive dancer. A knee injury curtailed it, though she later underwent risky surgery in order to dance again, this time on camera for the director . . . and her lover . . . Arnold Fanck. He was a distinguished maker of "Alpine films", a hugely successful genre, arguably equivalent to the America Western, which combined stunning scenery, uber-Romantic philosophy, climbing and skiing spectacle and absurdly overblown and sentimental plots.

Between 1926 and 1933 Riefenstahl starred in such vehicles as The White Hell Of Piz Palu and SOS Iceberg. By the time the last of these was made, she had already tried her hand as a director, with The Blue Light. The Weimar Republic had also come to an end and a new leader had emerged.

Riefenstahl's stock reaction when any influential new figure came on the scene was, "I must meet that man." Whether it was Fanck or Hitler, she always did.

A photograph of her greeting the Fuhrer at her Berlin villa in 1937 betrays some fascinating body language. He leans forward into a double handclasp while she arches away coquettishly.

Hitler thought she was partJewish, as she may have been, and if so it was a dark secret she may have shared with her admiring Fuhrer, who attracted similar rumours.

After the war, she seems to have believed that she could simply follow the pre-war exiles Ernst Lubitsch and Fritz Lang, or rehabilitated scientists and technicians such as Wernher von Braun, and make a new career in America. Hollywood failed to bite, though, and the former poetess of racial purity took on an ironic new role as the documentarian of the Nuba people of Sudan.

Her approach here was equally mendacious, inspired by a 1949 George Rodger photograph of an ash-daubed Nuba youth on another's shoulders. Riefenstahl claimed to have discovered and adopted the tribe herself: "my Nuba" is how she referred to them.

She was still there in 2000, filming during the civil war, still mad, bad and scheming, but still impressive, the oldest practising film-maker in history.

There have been books about Riefenstahl before, but Steven Bach benefits from writing after his subject's death and with access to materials and interviews which were not formerly available. He is an experienced biographer (of Moss Hart and Riefenstahl's contemporary Marlene Dietrich), who once ran worldwide production for United Artists . . .

so he knows the movie business inside out.

Unfortunately, he writes in a strange hybrid of slang and seriousness, awkwardly qualifying some of his more dramatic flourishes ("Movies were inevitable. Leni shared her crib with them . . . or nearly so . . . for the first exhibition of motion pictures before an audience had taken place, in Paris, in 1895, only seven years before she was born") and plucking at general points that never quite seem to deliver.

For all his faults, though, Bach tells a strong story, unflinchingly.

Riefenstahl had managed to edit her own life story as carefully as she once edited her own press book, trimming out all negative commentary and leaving in uncontextualised references to "genius" and beauty.

She was both, but she was also a schemer and as indifferent to individuality as the regime she served. This is a thoroughly deserved memorial.