'I made a great deal out of the possibility of incest,' says Mailer. 'People who are 'incestuaries' are either capable of extraordinary deeds or they will be terrible. As the genes are so close, you get a doubling of the possibilities, good or bad. I liked that notion, so I thought I'd go with it.'

Narrated by a former SS man, D.T., who functions like an aide-de-camp to the devil, the novel slowly reveals signs of early evil inculcated in the boy.

The main protagonist, though, is Hitler's father, Alois, an ambitious but poorly educated customs official whose libidinal wanderings contrast with Hitler's dutiful mother, a good-natured soul adored by her son. Mailer confesses that he grew fonder of the father's character as he wrote, but that he 'was fascinated with Hitler's mother, and that a woman, a good woman, could create such a monster'.

What The Castle and the Forest doesn't attempt to address are the social conditions that allowed Hitler's rise to power - the novel ends when Adi is 16. 'The real tests that greet Hitler are still ahead,' he says. 'He's a potential Hitler at that point. He's not a monster. He's a just a very unpleasant, diabolically ridden boy.'

Mailer has often used real-life characters in his work, and perhaps it's not surprising he would eventually turn to Hitler. Like many Jews of his generation, he has been living in Hitler's shadow since his youth and says he has wanted to write such a novel for 50 years.

'Hitler poisoned our optimism about civilisation - profoundly,' he says. As a result, Hitler is partially liable for similar evils perpetrated since. 'He was more diabolically inspired than Stalin, because Stalin you can comprehend in human terms - he was an ugly man who came out of an ugly, cruel environment. He may have killed more people than Hitler, but he was doing it because they were enemies. Hitler was killing by category, which is the most dangerous single thing you can ever do. It's a kind of vanity that goes beyond the limits of human vanity.'

Hitler isn't the first historical figure, demonic or otherwise, that Mailer has tackled. 'I tried with Jesus [The Gospel According to the Son, 1997] and by my own measure I failed, to put it charitably,' he says. 'He was just too big for me.'

The boldness to take on such grand and mythic figures may be rooted in the success of The Naked and the Dead. Published in 1948, when Mailer was just 24, his novel about war in the Pacific drew both on his combat experience and the stories of others thrust into the worst fighting. A sympathetic but unalloyed view of soldiering, the book was a publishing sensation.

At the time, Mailer considered his fortune a curse. 'But looking back on it, I think probably I was lucky, because - and I didn't realise at the time - I wasn't going to have to go through those painful and often destructive years that most novelists go through, where they have to work at jobs they detest for people they don't like and their talent is slowly being eroded. The only problem I ever had was to not violate my talents through excess of one sort of another, and that's a manageable ability in most people, including myself. I was able to think a lot. I was able to spend my life thinking. It was a blessing and I just didn't realise it.'

Managing the excess, however, wasn't enough. His next two novels - Barbary Shore (1951) and Deer Park (1955) - were critical and commercial failures. Mailer then turned to essays on sex, drugs, race and violence - at least three of which he was well qualified to write about. Many later appeared in Advertisements for Myself (1959). The controversial collection arguably affirmed Mailer as the leading essayist of his time and secured his place at the vanguard of what became known as New Journalism. It also included the short story A Time of Her Time, a sexually explicit, taboo-breaking story of an Irish Don Juan.

It was in non-fiction, though, that many felt Mailer had found his metier. For Armies of the Night (1968), an account of a 1967 march on the Pentagon, he was awarded the Pulitzer Prize for non-fiction. Soon, Mailer would move from writing about politics to participating, culminating in an unsuccessful run for mayor of New York City in 1969 on a secession ticket.

Now a self-described 'left-conservative' ('Don't ask me to describe it - I can't'), he never strays far from politics. Asked whether writers are born, as Europeans often assume, or cultivated, an American view, he can't hold back.

'One of our faults is that we tend to think that talented novelists and hothouse tomatoes are very much the same - in other words you can create both. America has this notion 'can do, will do'. In Iraq it was 'can do, will do', we'll bring those f***ing idiots democracy.'

So what does he think of the current president? 'Bush is the most ignorant president the United States has ever had!' he says. An allusion to Bush appears in The Castle and the Forest, when D.T. says of statesmen: 'They have installed in themselves an ability not to suffer sleepless nights because of casualties on the other side. They now possess the mightiest of all social engines of psychic numbification - patriotism!'

Not surprisingly, Mailer's writing has attracted criticism for more than its stylistic or narrative faults. Prisoner of Sex (1971), a response to the women's liberation movement, predictably inflamed feminists. That he had stabbed one wife, Adele Morales, didn't help. Germaine Greer labelled him - by then married and divorced several times - an 'alimony slave'. Gore Vidal, with whom he often traded words, was more stinging, calling the book 'three days of menstrual flow'.

Mailer's presence in much of his work has also drawn criticism. 'Mailer was blessed by the capacity to see deeply into post-war America's heart, but cursed with the need to write himself into its history,' Columbia University literature professor James Shapiro wrote in The New York Times. 'Too often he has one eye on the events, another on his role in shaping them. Rather than dissecting politicians or celebrities, he begins to size himself up against them.'

Shapiro, though, like many others, acknowledged that in The Executioner's Song (1979), a so-called true-life novel about convicted murderer Gary Gilmore, Mailer had written a masterpiece.

Responding to a question about the influence of Ernest Hemingway on his writing, it's apparent that Mailer remains proud of the Gilmore book - it won him another Pulitzer, this time for fiction - even if he shows a flash of uncharacteristic modesty.

'I reread Hemingway after I wrote The Executioner's Song. I thought I'd written something that was the equal of his style until I reread him and realised, no, he wrote better simple sentences than I did. He really was a great writer. He had a sense of English that's incomparable. He was not a great brain. He was rather an ordinary brain. And at times he was a damned unpleasant brain. But he was a great writer. He had more sense of the theme of a sentence than perhaps anyone who's ever written since Shakespeare. Perhaps. I don't want to cut myself off from other possibilities.'

One of those possibilities is indeed Mailer himself, who some believe belongs in the 20th century American literary firmament alongside Saul Bellow, Philip Roth and John Updike, although others, such as The New York Times' Michiko Kakutani, insist that non-fiction is his forte.

Another view is that Mailer's polymathic mind - he studied engineering at Harvard before starting to write - is too enquiring, even imaginative, to be bound by the novel in its truest form.

Although Mailer says he enjoys the solitary existence of the writer, he's equally at home in the public sphere. Like many literary stars, he was seduced by Hollywood. He made several movies, none of which matters, including an adaptation of his novel Tough Guys Don't Dance.

'What I enjoy the most is movie making,' he says. 'Unfortunately, I wasn't immensely talented as a movie director. But, oh, what fun it is! All the things that a man can't do in life he can do as a movie director. It's a wonderful feeling of power. The trouble is that you have to be successful over and over again.'

The world of books is kinder than Hollywood, and Mailer's failures have been tolerated as the necessary experiments of a fertile mind. So does he intend to follow The Castle and the Forest with something new?

'I'm going to be 84 in a week,' he says. 'I've watched people who go from 84 to 86 or 87. They get old at a very distressing rate. I'm much older now than I was three years ago. Assuming it takes three years to write another novel, I don't want to promise one. It may not happen. I'd be delighted if I could.'

He confesses that he finds Heinrich Himmler fascinating - the only one of the Nazis who had a truly original brain. What does he think led to Hitler's rise? Was it culture? Societal conditions?

'One of the great ironies is that the two peoples on earth who believe that culture was a solution to human and societal ills were the Germans and the Jews,' he says. 'They didn't have a belief in a similar culture. They each had a belief in culture. The culture that had the most profound belief in culture became the culture that violated culture the most. The Germans were a proud people, a cultivated, civilised nation. Hitler had an effect on Germany quite separate from the Germans.'

'How did Hitler succeed?' he asks rhetorically. 'I think you have to believe in Satanic inspiration.'

ON MAILER:

Truman Capote: 'He has no talent. None, none, none!'

Anthony Burgess on Ancient Evenings: 'One of the great works of contemporary mythopoesis.'

Gore Vidal: 'He is now what he wanted to be: the patron saint of bad journalism.'

Gore Vidal (Mailer having thrown a drink in his face): 'Once again, words fail Norman Mailer.'

Sinclair Lewis: 'The greatest writer to come out of his generation.'

MAILER ON:

'If a person is not talented enough to be a novelist, not smart enough to be a lawyer and his hands are too shaky to perform operations, he becomes a journalist.'

'I'm hostile to men, I'm hostile to women, I'm hostile to cats, to poor cockroaches, I'm afraid of horses.'

'I care about reviews - they affect your wallet in the most direct fashion.'

'The final purpose of art is to intensify, even, if necessary, to exacerbate, the moral consciousness of people.'

'Writing books is the closest men ever come to childbearing.'