Stacy Schiff was working as an editor at Simon & Schuster in New York when the idea first tiptoed into her brain. She had been rereading the works of Antoine de Saint-Exupéry, the French aviator who wrote the enormously popular fable "The Little Prince," when it occurred to her that his dramatic and too-short life would make a great book.

Schiff meant to suggest the idea to an agent for another writer to do, but something kept stopping her. "I started to get very possessive about it," she said. "There was this burgeoning obsession of not only do I want this book, but I actually would like to be the one to write it myself."

She began spending her lunch breaks poking around at the library, "and I just started falling down in the way that always happens with biography -- you become obsessed with someone else's life." It was a remarkable obsession for her; she had never intended to write a book. Twenty-one years later, she has written four, all biographies and each one widely praised.

The most recent, "Cleopatra: A Life," was the most challenging.

Schiff took on a subject who not only left behind no documents but who also had been written about hundreds of times.

The trick with any biography is to know that there is something new to say. But when she starts a new book, "I don't know," Schiff said. "Which is why I don't sleep at night."

First draft in longhand

Schiff's office is a block from the New York Public Library. It's where she plows through her bulging files of meticulous notes, writes and rewrites, stares out the window as she solves some particularly thorny riddle of a subject's life.

Her first drafts are in pencil on legal pad. "I type much faster than I think," she said. "The physical longhand slows me down. And also, there's just something about the pencil on the paper, the actual feel of touching the paper, that somehow is very gratifying to me."

Schiff, who is 50, travels between homes in New York and western Canada. She has three children, ages 11, 18 and 20, and a husband, Marc de La Bruyère, a businessman who lives in Edmonton, Alberta, whom she thanks in tender and humorous ways in her books' acknowledgments -- for always having a pencil, for exhibiting savoir-faire.

Schiff left Simon & Schuster in the spring of 1990 and sold the Saint-Exupéry proposal six months later. "It was thrilling! I can tell you precisely where I was standing!" she said. "There is a telephone in western Canada, in Jasper National Park." She had called her agent from the park and found out that her book had attracted several offers.

"Remember, I had a leg up -- I knew how to write a book proposal," she said. "So, of course, for the next three or four years I worried that I knew how to write a proposal, but not how to write a book."

That fear should be alleviated by now. Schiff's Saint-Exupéry biography was a Pulitzer finalist, and "Véra (Mrs. Vladimir Nabokov)" won the Pulitzer in 2000. Her third book, "A Great Improvisation: Franklin, France, and the Birth of America," won the George Washington Book Prize.

"Cleopatra" is just out in paperback and has won a PEN award. It has garnered thunderous praise, from everywhere. The Washington Post called it "a great, glorious spree of a story." The New York Times praised her verve, style and wit.

Never meant to be a writer

Schiff grew up in Adams, a town of about 8,500 people in the Berkshires of western Massachusetts.

Her father was a merchant and her mother a professor of French literature. Schiff was a reader, but not a particularly devoted one. "I had one of those childhoods that went in stages of falling in and out of love with books."

Still, after graduating from Phillips Academy and Williams College, she entered the world of publishing, working for Basic Books, Viking Press and Simon & Schuster, and serving as a consulting editor for the Paris Review.

She edited both fiction and nonfiction, including work by essayist Phillip Lopate, but she did not write on the side. "I wrote as much as any editor writes," she said. "Which is to say, I wrote flap copy and catalog copy."

After Saint-Exupéry, she turned her attention to Véra Nabokov, Benjamin Franklin and Cleopatra. She chooses her subjects by the questions they raise. "I would say ultimately it comes down to an obsession that you hope someone else might share," she said.

Each has presented a particular challenge. Tracking down Saint-Exupéry's former compatriots and girlfriends was difficult, pre-Internet. Benjamin Franklin left reams of journals and letters from his time in France, but most of it was written with an ulterior motive and so had to be decoded. Véra Nabokov was pathologically private.

The problem with Cleopatra

And then there was Cleopatra. "I'd been thinking a lot about women and ambition, and women and accomplishment, and Cleopatra stands at that crossroad," Schiff said. "This is sort of the ultimate brew of sex and politics, which seem to me to be the two subjects we still obsess the most about.

"It just seemed like there was a lot I could sink my teeth into there."

But there are no documents from her lifetime; papyrus, after all, deteriorates. The earliest accounts came from 100 years after her death, and, as with Franklin's papers, the authors had agendas and so their stories could not always be trusted.

On top of all that, everyone already thinks they know her.

"Many people have spoken for her, including the greatest playwrights and poets; we have been putting words in her mouth for two thousand years," Schiff wrote in "Cleopatra." "In one of the busiest afterlives in history she has gone on to become an asteroid, a video game, a cliché, a cigarette, a slot machine, a strip club, a synonym for Elizabeth Taylor. Shakespeare attested to Cleopatra's infinite variety. He had no idea."

The paragraph is classic Schiff; not just thoroughly researched and documented and fact-checked, but witty to boot. Later, when writing about Cleopatra gliding up the Nile (and please try not to picture Elizabeth Taylor here), Schiff compared her to both the Trojan Horse and the Beatles on "The Ed Sullivan Show."

That wry tone was deliberate, she told the Wall Street Journal. "When you are writing about a subject that's invisible or inert, the biographer has no choice but to come out from behind the bushes a bit more because you are having to animate ... your subject a bit more," she said.

But that's about as far out of the bushes as she is willing to creep. Her next book, "The Witches," will be about the Salem witch trials. At no time, she says firmly, will her next book ever be about herself.

"There is still a small part of me that would prefer to be behind the scenes and in the editor's chair," she said. "I've always wanted to write an essay about how the biographer leads two lives, the life he leads, and the life he understands. The reason I write biography is I don't have to meditate on my own life."