Like Michael Moore, Kitty Kelley is in a class all her own. Usually readers remember the subject of a documentary or a biography, but Moore and Kelley have investigated controversial and famous subjects in relentless and memorable ways that most contemporary filmmakers and writers would not dare or deign to attempt.

Kelley is often treated like a déclassé biographer. Unlike her more noble peers, she is thought to dwell on the seamy side of public figures' lives. But as Kelley herself points out in "Oprah: A Biography," her authoritative treatment of Oprah (Random House, 454 pages, $30), all biography is by its very nature invasive. What sets Kelley apart from others in her trade is her tenacity and charm. Just look at the photographs of her with Oprah's family members, and you will see that they invited her into their lives because they, too, have a story to tell.

That Oprah was ambitious, that she left behind her childhood friends and exaggerated her poverty and the hardships of her Southern upbringing are facts not presented in Kelley's biography as scandal. They are, instead, presented as the side effects of an understandable drive of a black woman who wanted everything the American dream has to offer.

To get at such a story -- one that is not merely the sort of glossy magazine profile that Oprah and her ilk are used to controlling -- Kelley has interviewed key sources and combed through countless records, even as she has used Oprah's own words to assemble a vivid account of how Oprah persistently pursued her career, patiently and sensitively responding to the television crews that made her look good and putting together a cadre of assistants to manage tabloids and other press outlets that craved stories about her.

Kelley's work exposes the hydraulics of fame. We watch Oprah transform herself from a journalist who aspired to be the next Barbara Walters to the talk show host who beat the reigning champion, Phil Donahue. Oprah built a new audience for herself and her medium, pioneering provocative and often sensationalistic programs about sexual abuse (including her own) and drug dependence (she confessed on air to her own crack cocaine addiction). And while doing so, she embedded her story into a kind of national soap opera, dramatizing serious issues that got her the ratings and respect she yearned for.

Seldom has a biographer been so well matched with her subject.

Carl Rollyson is a biographer and professor of journalism at Baruch College, City University of New York.