The good girl who found when she acted bad she was better

In a typically droll list of "Things I'll Never Do", Mae West insisted that she would "never try to be anything but myself at all times, publicly and privately, except on the stage and screen, for that's where acting belongs". West both failed and succeeded spectacularly in her ambition. She failed in that, like most iconic figures, she created a mask for herself that never slipped; she never stopped acting. She succeeded in that this mask seems to have been an extension of her own character. For nearly 50 years West epitomised the tough-talking, wise-cracking, man-eating vamp. And, as Simon Louvish reveals in his hugely entertaining biography, that is pretty much what she was, in private as well as in public. The mask was surprisingly transparent.

West was her own special creation, turning her skills as a writer to good use, carving out her own legend. From her days as a vaudeville turn, through her conquest of the Broadway stage, to her zenith as the greatest Hollywood star of the 1930s, West remained in total control, writing and performing the roles that made her a star. No other star of her generation created themselves to the degree that she did, and no other star of her generation courted controversy as assiduously as she did. West was regarded, in many quarters, as a tornado of filth and depravity who threatened to rip apart the moral fabric of American society.

Her work attracted the wrath of moralists across the country. Her plays were prosecuted for obscenity, her films censored and denounced. Of course, the public, ever in thrall to sensationalism, lapped it up.

West believed it was her duty to kick against society's constraints, a duty that repeatedly dragged her into territory that was deemed highly shocking.

In the 1920s, her Broadway plays, such as The Drag and The Constant Sinner , dealt with homosexuality and miscegenation. West's treatment of these themes - truly subversive at the time - has seen her reappraised, in recent years, as a gay icon and as a black woman in a white body. But even the most cursory reading of these plays reveals that West did little more than reflect the prejudices of her age. Her black characters are primitive and dangerous; the gay men are only happy when wearing frocks. West even declared lesbianism "unnatural" and was appalled when a lesbian film star made a pass at her (Louvish guesses that the would-be seductress was Marlene Dietrich).

But it was not these horrifying themes that made West such a transgressive figure. Instead, it was the image that West put across that turned her into the moralists' pariah. The problem can be summed up in one word: the title of her 1926 theatrical cause célèbre, Sex . In it, West played a prostitute who was assertively and unapologetically sexual, a woman acting like a man in the sexual arena, in control of her own sexual destiny. And for middle America this was far too much to stomach. The play was raided by the police, West was prosecuted for obscenity and jailed for eight days (she got two days off for good behaviour).

It was this scandalous role that West repeated - with minor variations - throughout her career. Once she had scandalised Broadway, she took the act to Hollywood, where even the mention of a Mae West script got the newly created film censors hot under the collar. Her films made it to the screens only after a tough battle between the studios and the censors. West was repeatedly forced to rein in her act, resorting to innuendo to make her point.

But the actor was not being provocative for the sake of it. She believed she was blazing a trail for women, opening their eyes to the truth about sex, putting an end to puritanical ignorance. And in her way she was an important feminist figure, carving a career in a man's world by adopting male sexual mores. Louvish reveals that she was sexually liberated and thirsted for sex with many partners, including a high number of boxers and gangsters. West was pretty much playing herself.

After West spent the 1920s as the queen of Broadway and the 1930s as the highest paid actor in Hollywood (at one point the highest paid person in America), the work began to dry up. She was simply too old to be believable as a sexually rapacious blonde beauty. The work may have stopped, but the Mae West act did not falter. Instead, she became a living legend, the mask hardening into a self-parodic grimace. By the time of her comeback in 1970 at the age of 77, she was like a living waxwork, sticking rigidly to the West script. She received interviewers in her boudoir, published a book of sex tips and refused point blank to play any role over 26. Fifty years after its conception, the Mae West mask was still shatterproof despite the blatant absurdity of an old woman coming on like a 20-year-old. But then, what else could she do? The public and private acts of Mae West had become so closely intertwined that she did not know where else to turn. As she put it herself with characteristic perception, "I am captive to myself".

Robin Dashwood is a television drama and documentary director at the BBC.