Four times married and with two grown-up children in the United States, Hopkins has lived in Thailand since 1993, and his Bangkok apartment nestles on a restful downtown side street. Fragrant frangipani blossoms float over garden walls, and scarlet-backed flowerpeckers, white-vented mynas and other tropical birds perch in its knotted banyan trees. With his thinning grey hair and trimmed beard, thick spectacles, beige slacks and gaudy, open-necked shirt, the writer has the avuncular air of a retired civil servant.

A short stroll from Hopkins' hideaway, however, lies the Thai capital's main sex-tourism drag of Sukhumvit Road, where street-side stalls ply hardcore porn DVDs and Viagra (about 10 bucks for four of grandpa's little helpers), as well as chromed knuckledusters, ninja throwing stars and equally dangerous-looking sex toys.

"Being a bottom feeder has a long literary tradition," says Hopkins. "There's a whiff of danger about Bangkok. I hate to romanticise dirt, but we're talking whores and drugs and the fun things in life. Life's more fun as a bottom feeder."

Over almost half a century, Hopkins has delivered three-dozen books covering everything from rock-chick groupies and the history of the condom to spoof astrology. He has, by his own admission, enjoyed an unconventional career by chasing down the bizarre. Originally rejected by 30 publishers over seven years, - the first rock biography to reach No1 on best-seller list - has never been out of print since 1980, selling in the millions worldwide.

"Morrison was the most interesting of all the rock stars I met because he was the best conversationalist," Hopkins says. "Something I always had trouble with at was that I was interviewing people whose avenue of communication was singing or playing an instrument. Why should anyone expect them to have a political opinion worth listening to? Most of them didn't, but Morrison was interesting on a totally different level."

Hopkins pours two glasses of iced tea, changes the battery in his hearing aid and sits to reminisce on sex, drugs and rock 'n' roll; of offbeat rocker Frank Zappa's "musical bicycle", of the blame the writer gets for the conspiracy theories surrounding Morrison's perplexing death in Paris at the age of 27, and of his personal taste for trans-sexual street hookers. We begin in the year The Doors signed their first record deal. The soundtrack to that heady 12 months featured The Byrds' , Bob Dylan's and The Beatles' .

"1966 was a great year," says Hopkins, recalling how he had embraced the countercultural zeitgeist. "I guess 67 was the Summer of Love, but 66 was when all the great records came out. Things were getting terrible in Vietnam, and civil rights was bubbling away, but we thought we were gonna change the world. We really believed that, and I don't think any generation since has shared that level of … I would prefer to use the word 'positivism' as opposed to 'naiveté'."

In 1966, Hopkins and a friend opened what was only the third "psychedelic store" or "head shop" in the US. LA was a headquarters for the prevailing drug culture, and so that was chosen as the name of their store. "Headquarters was the first head shop in Los Angeles. I didn't even know what a head shop was."

Hopkins' shop quickly became a community centre for the hippy generation. "Kids would hang out in the afternoon so they didn't have to go home to mom and dad," he says. "They could be with these hip guys who openly sold rolling papers. We sold lapel buttons, which were a big thing at the time: 'Save Water, Shower With a Friend', 'Even Paranoids Have Real Enemies', and the like. We had Peter Fonda posters, Bob Dylan posters; and a selection of maybe 15 underground newspapers from across the country. When the brass band of [minor league hockey team] the Los Angeles Blades changed their uniforms, we got the old ones. We sold them as Sergeant Pepper uniforms. Harrison Ford, an out-of-work actor and carpenter at the time, sold us Fillmore dance posters."

It wasn't long, however, before similar stores were sprouting like magic mushrooms from coast to coast, and Hopkins takes the "blame" for their proliferation: "Headquarters had been open for about six months when I was quoted in as saying, 'We're gonna gross US$50,000 this year if things continue as they're going.' I could just hear dopesters all over the country saying [adopts a clichéd stoner voice], 'Hey man, let's open a head shop.'"

Hopkins' long and strange trip from his Quaker roots to Californian bohemia was set in motion by conflict rather than peaceniks.

"During the second world war, I would read the dispatches of [Pulitzer Prize-winning correspondent] Ernie Pyle. He covered Europe and then the Pacific. He died in the Pacific, in fact. I decided that was what I wanted to do when I grew up: travel the world, meet interesting people, write about them and get paid for it. I was aged nine then, and I've never wavered."

After university in Virginia, a graduate degree from Columbia University in New York, two years at a newspaper in New Orleans and a stint in the army in Georgia, Hopkins found himself back in the Big Apple.

"I worked as a writer-producer on a Mike Wallace show, but it never really got traction or an audience, so it got canned," he says. "Mike went on to much greater things at CBS, and I was asked if I wanted to go west to work for Steve Allen, who'd invented . It was 1962. I was in a marriage that wasn't working. Hell, she had thrown me out and I was sleeping on a friend's couch, so I headed for LA.

"Steve needed somebody who could come up with an off-the-wall person, or an act, that he could bounce off for comedy effect, five nights a week. So I became his 'vice-president in charge of left-fielders'. I was Steve's 'kook-booker'. Some of the people were genuinely strange."

Finding eccentrics for the new proved easier than Hopkins had imagined, and he searched out zany nonconformists from the proto-hippies, "health weirdos" and other subcultures edging into the Californian mainstream in the 60s. One was a pre-fame Zappa.

"He called [in 1963] and told me he wanted to teach Steve 'musical bicycle'. I knew it was a put-on, and Steve had always insisted no put-ons, but Frank sounded interesting, so he came along. He played the spokes like a harp. He beat on the seat and blew at the handlebars. He would not admit it was a joke. Then, years later [in 1966], suddenly here comes Frank Zappa. He's got long hair and a funny Zapata moustache and a new album called "

Having become disillusioned with television, and later with the head shop suffering financially ("The big department stores started taking our business - if you wanted a poster of Peter Fonda, you could get it at the May Company"), Hopkins found himself at a loose end. But another golden opportunity would soon present itself to Jerry Gump.

"Back then, was a twice-monthly newspaper, tabloid size," Hopkins says. "I'd seen a box in one of the early issues - we sold in the store. They were soliciting for freelance submissions, so I sent in a review of a Doors concert. They printed it and sent me a cheque for US$15. I thought, 'This is terrific.'"

Hopkins became 's LA correspondent.

"That first article [about The Doors] was a little critical. I called Jim pretentious. He deliberately threw himself into the audience and I thought that was a little precious, but I really liked their lyrics and I really liked Morrison. We drank in the same bars and he would invite me to poetry readings and screenings and stuff."

Hopkins gleaned many personal insights into Morrison while covering the LA music scene, and film director Oliver Stone used Hopkins' interview notes, as well as , as the backbone to his 1991 biopic . The movie's release resulted in the biography bouncing back to the top of best-seller list, this time to the No2 spot, but the writer is conflicted about Stone's cinematic portrayal.

"The look of the movie was bang on," Hopkins says. "It was like being whip-lashed into my past. Oliver had every-thing very accurate visually, which is interesting [considering that] 40 per cent of the screenplay turned out to be total fiction. It's true that Jim was a drunken asshole, but that wasn't all he was. He read more books and was more articulate than anyone else I've ever met in the entertainment world. He had a sense of humour about himself. He didn't take his stardom seriously. He was a poet. He was a lot of things that Oliver ignored."

According to the French police report on Morrison's death, the singer's girlfriend, Pamela Courson, found him dead in the bathtub of their Paris apartment on July 3, 1971, apparently having suffered a heart attack. Morrison was quickly buried in the French capital's Pere Lachaise Cemetery. Conspiracy theories regarding the exact circumstances have multiplied ever since.

"I get blamed for this," says Hopkins. "My original plan had been for two different final chapters [to ]. One ending would have Jim overdosing on a combination of heroin and alcohol. [In the second version] he faked his death and, like his idol, the French poet Rimbaud, he wandered off to North Africa to gain the freedom that anonymity would give him. He was fed up with being a star.

"I suggested that if the publisher were to print 10,000 copies of the book, 5,000 should have one ending, and 5,000 the other. Distribute them and don't say anything, which I still think is an interesting concept. [The publisher] said that was too much trouble, and to put the two chapters together, end the book ambiguously, which I did. So now, many people say that book created the controversy over whether Morrison is dead or alive, and of how he died, and blah, blah, blah."

Hopkins insists that the true cause of Morrison's death had been "very well established long before my book came out", and that he is not culpable for crackpot theories.

"America lets go of its heroes reluctantly," Hopkins says. "It's quick to build them up and slap them down, but it doesn't want them to die."

At the time of Morrison's death, Hopkins had just wrapped up , which he had, in fact, undertaken on the personal suggestion of Morrison, who had been fascinated by Presley. In 1972, with that book on the shelves, the writer rejoined and was soon sent to cover the British music scene from London.

"It was the year after Morrison died, and I went over to Paris to research his death," Hopkins says. "Everybody I spoke to told me he'd suffered a heroin overdose in the Rock'n'Roll Circus nightclub, and that he had been carried home. Well, what do you do when somebody has an overdose?"

Hopkins says a bath of cold water was commonly considered helpful to drug users suffering from a surfeit of heroin. "And that's where he died, in a bathtub. But the truth would have caused problems for others present, so they created this lie that he'd had a heart attack. A doctor came and there were no signs of violence or foul play. It was the Fourth of July weekend, which was no big deal for Paris, but the American Embassy was closed. [Morrison] was in the ground in a hurry."

Hopkins admits, however, that he is still troubled by Morrison's reported use of heroin.

"That had not been his drug," insists Hopkins. "Jim did do a lot of cocaine, but his drug of choice, since long before he died, had been alcohol. In my interview with him in the early summer, after the Miami arrest [for indecent exposure onstage] of March 69, he said that he had switched to alcohol because it was so much easier to obtain [than illegal drugs]. You just walked into a store, put your money on the counter and they gave you a bottle. He didn't want the hassle anymore."

Though , which been translated into 16 languages, has made Hopkins royalties for 32 years and counting, he insists he has not lived off the proceeds alone.

"I think I've been paid for two million [copies]," he says. "The publisher of the English edition alone told me that she had sold a quarter of a million. I think the accurate sales figure is four [million] worldwide, but I don't know."

So how much money has his best-seller made him? "I have no idea." Millions? "Hell, no. I've lived comfortably, and I tried to shovel as much of it up my nose as I could, living well beyond my means at times. I ended up in bankruptcy court [in 1986] and divorce court [from his third wife, having moved to Hawaii in 1976]. I haven't had a credit card ever since, so some good came of it. My feeling now is that I didn't take to being rich, and my idea was to get poor again as soon as possible, so that I could be happy again."

Hopkins rediscovered his happiness in the arms of Vanessa, a transsexual hooker of Polynesian descent who worked the streets of Honolulu's Chinatown.

"I was in love with her, I shared my bed with her, on the nights when she came home," he says, chuckling at the memory. Hopkins has been "totally fascinated with that lifestyle" ever since.

With light fading, we decamp from the writer's bolthole to stroll Sukhumvit to Nana Plaza, Bangkok's neon-lit warren of go-go bars and clip joints that is arguably the largest single compound of paid-for sexual gratification on the planet. We order beers and survey the spectacle that Hopkins described in an earlier e-mail as "what Morrison called 'the soft parade', in this instance the whores going to work, the men streaming in after them, the first exiting on 'dates'".

The pleasingly anarchic Thai capital, Hopkins insists, is inspirational to his work. When not trawling licentious Bangkok, however, he lives with his fourth wife - who is Thai, 25 years his junior and whom he met in Nana - and her extended family on an idyllic rice farm close to the border with Cambodia, and a six-hour drive from the city.

"We have 12 types of fruit, four fish ponds," says Hopkins. "We raise frogs, chickens, ducks … It's quiet. We have no telephones, no internet."

Thailand, with its contrasting extremes, appears to be the right place for this time in Jerry Gump's deliberately unorthodox life.

"I'm researching two books at the moment," enthuses Hopkins, who recently penned the introduction to a forthcoming volume entitled - a compilation of poetry by tough-guy actor Michael Madsen. "One is about ladyboy sex workers, and the other is called ."

Hopkins carries out much of his "research" at Cascade, a go-go bar that is headquarters for more than 100 transsexual prostitutes, including, he laughs, one chisel-jawed individual whose nickname is "Lights Out", not for her after-dark activities but for her devastating Muay Thai skills in silencing difficult customers.

"All of that strikes me as a hell of a lot more interesting," the kook booker says, "than what my daughter calls a 'real job'."