Rowling calls her time with Harry "one of the longest relationships of my adult life," her rock through bereavement, a turbulent marriage and divorce, single motherhood, changes of country, fear of failure — and transcendent joy, on the day a wise man at Bloomsbury offered her $2,250 and agreed to print 1,000 books. When Harry Potter and the Deathly Hallows went on sale last July, it sold 15 million copies worldwide in 24 hours, breaking the record that had been held by each of the previous three books. (To put that in perspective, 2005's Half-Blood Prince moved more copies on its first day than The Da Vinci Code did in an entire year.) Meanwhile, the movie version of Book 5 — Order of the Phoenix — made $645 million, and plans for an Orlando, Fla., theme park were unveiled. Forbes magazine put Rowling second only to Oprah as the richest woman in entertainment, ahead of Martha Stewart and Madonna — and as the first person to become a billionaire by writing books.

And that is on top of the impact, even her critics acknowledge, of inspiring a generation of obsessive readers unafraid of fat books and complex plots. "They're easy to underestimate because of what I call the three Deathly Hallows for academics," says James Thomas, a professor of English at Pepperdine University. "They couldn't possibly be good because they're too recent, they're too popular, and they're too juvenile." But he argues that the books do more than entertain. "They've made millions of kids smarter, more sensitive, certainly more literate and probably more ethical and aware of hypocrisy and lust for power. They've made children better adults, I think. I don't know of any books that have worked that kind of magic on so many millions of readers in so short a time in the history of publications."

The ending, naturally, was the most controversial part of the book. It would have been so much neater just to kill Harry. "I've known that all along," she says, but that was never her plan. To her, the most noble thing, the real bravery, is to rebuild after a trauma. Some fans were disappointed that after all his adventures, Harry's greatest concern in the end is whether his son will fit in at Hogwarts. "It's a bittersweet ending," she says. "But that's perfect, because that is what happens to our heroes. We're human. I kept arguing that 'love is the most important force, love is the most important force.' So I wanted to show him loving. Sometimes it's dramatic: it means you lay down your life. But sometimes it means making sure someone's trunk is packed and hoping they'll be O.K. at school."