BE AFRAID, be very afraid. Kitty Kelley is going to write the unauthorised biography of Oprah Winfrey. A couple of things could happen. Kitty Kelley could end up sleeping with the fishes, murdered by an outraged Oprah. Oprah could be outed as, amongst other things, gay. But for the American book industry, the most terrifying prospect of all is that Oprah could refuse to promote any more Random House books on her show.

Crown, the imprint which announced on 13 December that Kitty Kelley is to turn her intimidating attentions to the subject of the US's most powerful woman, is owned by Random House. It is a sign of Kelley's enormous reputation as a bestselling author that the company has agreed to unleash her on Oprah.

Meanwhile, back in chat-show land, Rosie O'Donnell, once a talk show host herself, has claim on US television that Oprah and her very best female friend, Gayle King, "might be a little bit gay". Lawks.

Kelley has spoken comparatively warmly of Oprah saying that "she has fascinated me for many years".

But for Oprah . . . who has a stormy past which includes being sexually assaulted as a child and several lawsuits taken by former employees who claimed that she had bullied them . . . the proposed book is not such great news. It was Kelley who likened the Bush family to the Corleones.

But Oprah would be well advised not to sue. Frank Sinatra tried that when Kelley wrote her unauthorised biography of him, back in 1986. His Way: The Unauthorised Biography of Frank Sinatra was . . .allegedly . . . a devastating read.

Sinatra slapped a $2m law suit on Kelley and her publishers, but he still could not stop the book appearing. In the end, his $2m just bought Kelley and the book free publicity. The book revealed Sinatra as a misogynistic bully, and firmly linked him to the Mob.

Kelley has demurely said that her books are a process of "moving an icon out of the moonlight and into the sunlight". It certainly seems that the icons don't like the journey . . . and nor do their loved ones. Nancy Sinatra famously said of Kelley: "I hope she gets hit by a truck."

But Kelley is alive and well and working harder than ever. "I'm a worker bee, " she has said. Opinion on her is sharply divided. She is called a celebrity biographer, an accurate if not exactly respectful description. She has even been the subject of an unauthorised biography herself, Poison Pen, by the conservative journalist George Capozi Jnr, published in 1991, the same year that Kelley brought out her book about Nancy Reagan.

Kelley is a gossip-monger and her many critics like to say that people read her books in the same way that they read The National Enquirer. Like all the best gossip, some of Kelley's stories are so good it almost does not matter if they are true or not. For example, in her biography of Nancy Reagan, which became the fastest selling biography in publishing history, she claims that Nancy was so mean that when a grandchild of hers lost a teddy bear on a visit to the White House, she returned it to him, wrapped up as a Christmas gift.

The hatred that the American right reserves for Kelley is unbounded. When The Family: The Real Story of the Bush Family came out, shortly before the 2004 presidential election, the White House tried to prevent her being interviewed on television.

In the end, Matt Lauer of the Today programme gave her such a hostile interview . . . pressing her to say who she was going to vote for, trying to out her as a liberal . . . that it backfired on him and on his programme.

In a country with the most hard-working media in the world, Kelley has never once been successfully sued for libel. All her books are assiduously picked over by a sceptical press for errors. With the Jackie Oh! book, in which Kelley was one of the first to detail JFK's womanising and Jackie's depression, it turned out that Kelley had claimed she had interviewed JFK's brother-in-law, the actor Peter Lawford, 12 days after the man had died. Kelley boasts about how many interviews she has conducted for each book: 857 for Sinatra; 1,002 for Nancy Reagan and so on. But the truth is that she has included some howling errors, and been let down by her sources. In 1990, she wrote up an interview with Judith Exner, an exlover of Sinatra, for Peoplemagazine. It turned out that Exner had been paid $50,000 for the interview and had been terminally ill at the time.

When Kelley wrote about the Bush family, claiming that George W had sniffed cocaine in the White House when his father was in office, her main source in the Bush family, Sharon Bush, the traumatised ex-wife of the womanising Neil Bush, recanted and said that Kelley had duped her.

Still she is a tireless worker who always manages to turn up something new on subjects that other biographers would dismiss as over-exposed to scrutiny. She is said to have gone through Elizabeth Taylor's dustbins as part of her research.

She has been right about a lot . . . for example, Nancy Reagan's reliance on astrology. As American journalist Sally Denton has pointed out: "The irony here is that Kelley is more of an embarrassment to the media than she is to the Bush familyf She may turn out to be the Mary McCarthy of sleaze."

As a young woman, Kelley was allegedly fired from her job at the Washington Post when she was observed taking what the London Times has called "unnecessarily detailed notes when the newspaper's proprietor spoke at meetings". Her first book, Glamour Spas, was an expose of the healthfarm industry.

Then she came out with Jackie Oh! . . . she had found her role. For a woman whose childhood had been made a misery by an alcoholic mother, there may have been some satisfaction in demolishing idols.

Yet even her enemies acknowledge that Kelley reaches a basic truth about most of her subjects. Crucially, she learns along the way.

One of her sternest critics, Jonathan Yardley of theWashington Post, said that His Way: The Unauthorised Biography of Frank Sinatra "is such an improvement on her two previous books that comparisons border on pointless".

But such faint praise is patronising. At the time of the Bush biography, when the Republican party had its guns turned on Kelley, Sally Denton listed the names that Kelley had been called. Catty Kelley, Kitty Miaow, the Scandalista, Kitty Litter, and so on. Most of the insults are sexist.

It is hard to think of a male author, of Kelley's age, who would find their work or their person belittled so routinely. It may be a tribute to Kelley that she makes the media as uncomfortable as she makes her subjects. And, of course, there is the fact that she has made millions and millions of dollars. Oprah better watch out.

C.V.

Occupation: Biographer
Born: 4 April 1942, Spokane, Washington State.
The eldest of eight in a prosperous Catholic family. Mother alcoholic
Education: Obtained B.A. in 1964. Worked for Eugene McCarthy for two years
Career: Editorial assistant at the 'Washington Post'. Unauthorised biographies of Jackie Onassis, Elizabeth Taylor, Frank Sinatra, Nancy Reagan, the British royal family, the Bush family
Married: To novelist Mike Edgley (dissolved 1989). To Jonathan Zucker, a physician
In the news because: She's stepping into the ring with Oprah