Norma Jean take 601...

Please don't make me a joke. End the interview with what I believe. I don't mind making jokes, but I don't want to look like one." So said Marilyn Monroe in a Life interview published the day before she took an overdose of barbiturates, aged 36. In her appeal to the interviewer and indirectly to her audience, Monroe herself begs the question, at once coquettish and controlling, that biographers have tried to answer ever since. What did she believe? What did she want you to believe? Could you believe her? Who was she?

Sarah Churchwell's answer to the over-ripe field of Monroe studies - some 600 books and scores of articles plus documentaries, plays, novels and an Elton John song - is a critique of the posthumous Marilyn: a Marilyn recreated in words. The Many Lives of Marilyn Monroe is a critical biography of the biographies or, as Churchwell calls it, a "story of the stories" that seeks to show how the beliefs and prejudices of others have shaped each successive portrayal of the "most famous dead woman in the world".

Few facts are known. Even her name is unclear: it was Norma Jeane or Norma Jean, Mortensen, Mortenson or Baker - depending on whether you believe her birth certificate, baptismal certificate or her first marriage licence.

With such an abundance of sources, Churchwell, a lecturer in English and American studies at the University of East Anglia, inevitably singles out some of the heavyweights for close scrutiny. Norman Mailer's Marilyn is shown up for the judgemental "novel biography" it is, relying more on fantasy than fact. Gloria Steinem's Marilyn: Norma Jean , Arthur Miller's play After the Fall and later biography Time Bends also share the spotlight. Churchwell (who admits she is a blonde) is especially disparaging of Joyce Carol Oates' Blonde , ridiculing the reductive portrait of a "dumb blonde".

Deftly, she makes clear what is not true, exposing cliché and conspiracy, refusing to give credence to some of the more salacious and murky rumours surrounding Monroe, in keeping with the academic tone of the book. But more enlightening are the one-off opinions of those who worked with her, which open up the debate. Jean-Paul Sartre said that she was the greatest living actress. Eve Arnold, the photographer, explains "how she had learnt the trick of moving infinitesimally to stay in range, so the photographer need not refocus but could easily follow movements that were endlessly changing".

On a more personal note, the director John Huston comments that "she was observant and tough-minded and appealing but she adored all the wrong people and she was recklessly wilful... You couldn't get at her."

Getting at her - the desire to purposely hurt or simply to get to know her - is precisely the fascination and challenge of Monroe. Her currency was always her ability to appeal to everyone: to be the model, the homespun girl, the movie star, the wife, the abused child, the victim, the diva and so on - a shifting mix of fact, fiction and fantasy. A silhouette of America in the Fifties that each individual fleshed out with their own version.

Churchwell's strength is in proving just how difficult the task of biography can be. Her thorough research and intricate analysis provide an invaluable study of textual reference. However, little of it is done with primary sources. Nonetheless, The Many Lives of Marilyn Monroe is a fair and detailed introduction to Monroe and all those who have tried to know her.

Helen Davies works for The Sunday Times .