The power of nightmares is hard to resist. Nightmares about monsters on the prowl, about technology turning against us, about scientists trying to play God. So far, so thrilling, as long as you then awaken in the cold light of morning. It's when bad dreams get confused with real life that their purveyors become insidious.

Michael Crichton, author, film director and father of the 'techno-thriller', what keeps you awake at night? 'Unfortunately, my nightmares are disappointingly dull,' he once confessed. 'I can't get the computer code right; I can't find my way through the train station; I am trapped at a tedious cocktail party and can't leave; I can't remember the names of people I meet. Ordinary life events.'

Yet his is the imagination that brought dinosaurs back to life in Jurassic Park, explored the violence of nature in Twister and conjured a swarm of killer micro-robots in Prey. His new novel, Next, finds its scare story in biotechnology. As the dust jacket breathlessly sells it: 'Talking chimpanzee reported in Java ... A group of tourists in Indonesia swear they were abused by a talking ape in the jungles of Borneo ... New transgenic pets on horizon ... giant cockroaches, permanent puppies ...'

Away from the fantasies, this is also a man who had a deeply flawed relationship with his father, has been through four divorces, been robbed at gunpoint in his home and nearly found himself in the wrong plane at the wrong time on 11 September 2001. But in some people's eyes the seemingly amiable giant (6ft 9ins) has forfeited all right to sympathy by becoming the poster boy of climate change denial, accused of mixing science fact with fiction and pouring crackpot opinions in the ears of fans including the one who really matters: George Bush.

Crichton cites his major influences as Arthur Conan Doyle, Mark Twain and Alfred Hitchcock. He is no prose maestro, but can match anyone at hitting the public's sweet spot, having sold more than 150 million books and seen 13 of them turned into films. Shakespeare might be immortalised by a theatre or two, but not even he can claim to have a dinosaur named after him; the 64-year-old can point to a fossil christened Crichtonsaurus bohlini in 2002.

His status as one of the world's wealthiest writers - about £70 million is regarded as an unspectacular year - has not come easily. He works a seven-day week, rising at 6am and staying increasingly late at the office as each book progresses. One of his editors says: 'Whatever the word is that's the opposite of lazy is what Michael is.' He claims to have 30 potential ideas for books buzzing in his brain at any one time. Shortly before they divorced, his fourth wife, Anne-Marie, publicly complained that his workaholism left her feeling abandoned: 'It's like living with a body and Michael is somewhere else.'

Writing is in the DNA. The son of a journalist, Crichton grew up to the clatter of a typewriter, 'so it seemed like a normal occupation, to sit down and type something as your job'. As a child he wrote scripts for his friends and became the school swot. He recalls: 'I was the weird kid who wrote extra assignments the teacher didn't ask for. I just did it because I liked writing so much. I was tall and gangly and awkward and I needed to escape, I guess.'

Home was not necessarily a refuge: he once described his father as a 'first-rate son of a bitch'. When John Crichton died, his son was reluctant to attend the funeral. The recollection in his memoir, Travels, is possibly the most shocking passage he has ever written: 'Somebody had to remember, in the midst of all these maudlin carryings-on, that the guy had a really nasty streak in him. What about the time he beat up my sister so badly the doctor was going to call ...' The sentence remains unfinished, and he has agreed with his family not to talk about his father in public again.

At 14, he had an article in the New York Times travel section and wrote for the student newspaper at Harvard, where he studied English, only to find his writing style damned by a tutor with grades of C+. In what he describes as a scientific experiment, Crichton submitted an essay by George Orwell under his own name. It was marked B-.

In despair, he switched to anthropology, then went to Harvard Medical School, where he paid his way by writing paperback thrillers. In 1969 he broke through with The Andromeda Strain, about a space virus unleashed on Earth, which he later sold to Hollywood for £100,000. Significantly for future works, he was advised by his editor, Bob Gottleib, to rewrite his first draft so that it read as convincingly as a profile in the New Yorker. So a career of cloaking fantasy in the trappings of apparent reportage was under way, which caused trouble when Orson Welles made his radio broadcast of The War of the Worlds, and has got Crichton into hot water of his own.

He caught the Hollywood bug and wrote and directed Westworld, about a Wild West theme park that goes haywire, pioneering the use of computer-generated special effects 11 years before The Terminator, with Yul Brynner's robot assassin prefiguring the Arnold Schwarzenegger character. But it was Jurassic Park, the writing of which was fuelled by daily sushi - he sticks with a favourite meal for each book - that gave him his Da Vinci Code moment. Again, a theme park gets horribly out of control, but this time the predators are dinosaurs cloned from prehistoric DNA.

The film adaptation, directed by Steven Spielberg, grossed more than $900m worldwide. It marked a giant leap forward in computer animation to the era of The Lord of the Rings. Some felt that it was anti-science, others that it would ruin the art of film-making. A typical view: 'Everything is a financial calculation. Movies have become these loud, noisy, largely impersonal effects-driven theme-park rides ...' Extraordinarily, this remark came from Crichton himself; he sought to clarify matters by saying that he missed the smaller stories, 'those Tracy and Hepburn pictures', which are now 'all going to television'.

His own attempt to use the small screen for storytelling without giant beasts or bangs was a tremendous hit. ER, drawn from his training as a physician, proved the making of at least George Clooney. Crichton was once more concerned to give his tall tales the ring of truth: 'One of the things that distinguishes that show from other television shows is the degree to which it is based on real stories. Viewers can tell.' His novel Disclosure, in which a company executive sues his female superior for sexual harassment, was also based on a true story. It became another starry film with Michael Douglas and Demi Moore, earning the scorn of feminists.

Four marriages ended in divorce, the last one costing him a settlement of £20m, his New York estate, fine art collection and 20 horses. He agreed joint custody of his only child, a teenage daughter, Taylor. She was with him four years ago when intruders broke into his surprisingly modest bungalow in Santa Monica, California. Crichton woke to find himself staring at a handgun and two masked men standing over his bed. He and his daughter were tied up and robbed. He said of the experience: 'It makes me more accepting of the use of force to stop bad guys. I find now that I can support things like the war on Iraq. It's made me a lot more hawkish.'

Another narrow escape came on 9/11. Crichton was on an American Airlines flight that left New York for Los Angeles at 8am. When the plane was ordered down, he called his office to be told everyone was in tears, convinced that he was dead.

This blurring of fact and fiction, for so long a winning hand, began to look less clever in 2004. State of Fear was an environmental thriller which portrayed global warming as a scientific hoax used to justify acts of eco-terrorism. On his slick website, Crichton, apparently without irony, includes in his list of personal accolades: 'The American Association of Petroleum Geologists Journalism Award, 2006 (State of Fear).' He is still beating the drum, giving speeches about 'environmentalism as a religion' and writing how 'consensus science' on climate change echoes the once widespread belief in eugenics. He told an interviewer last year: 'People say our grandchildren will loathe us, but they will also loathe us if we waste trillions of dollars tackling a problem that is non-existent.'

Even fellow sceptics such as Bjorn Lomberg have distanced themselves. But the star author was invited to the White House to share his insights with Bush, said to be a fan of the book, causing alarm among environmentalists.

Fabulously wealthy, profoundly successful and undoubtedly handsome, Crichton has reasons aplenty to be content. Yet when most people are poised for retirement, the workaholic appears to have embarked on a journey from popular thriller writer to political maverick. If power comes with responsibility, he may have exploited the power of nightmares once too often. Don't look for repentance in his new book, which declares up front: 'This novel is fiction, except for the parts that aren't.' The two can be painfully difficult to separate.

The Crichton lowdown

Born

Chicago, 23 October 1942, the eldest of four children. His father, the editor of a New York advertising journal, was drafted to fight in the Second World War, leaving the family in small-town Fort Morgan, Colorado. They then moved to Long Island, New York, where Crichton grew up and went to school.

Best of times

The mid-Nineties, when he could make the unique boast of simultaneously having America's number one film, Jurassic Park, number one bestseller, Disclosure, and number one TV series, the Emmy award-winning ER.

Worst of times

Grilled last year by the US Senate over his scepticism about climate change. Rebuked by Hillary Clinton for views that 'muddy the issues around sound science', and by Barbara Boxer, who said: 'I think we have to focus on facts, not fiction.'

What he says

'Writing a book is a bit like going on location for a movie. You're absent from your life, your family, and your friends. You're psychologically gone, so you might as well be physically gone.'

What others say

'He's encouraged people to think man-made climate change isn't a reality. I receive a lot of emails saying, "I've just read State of Fear and you're part of a global conspiracy." When you confuse science fact with science fiction you have a licence to believe anything.'

George Monbiot, the writer and environmentalist