'THE first time I went to rehab, I got a job.

The head of a big US production company was in there. It was great."

Is David Hasselhoff the greatest self-promoter on the planet, as his ex-wife alleges? Or will he simply say "yes" to anything?

Audiences can find out next month when the US celebrity brings David Hasselhoff Live to the Edinburgh Fringe, an all-singing, all-dancing, interactive "runaway train we call 'From Baywatch to Broadway to Berlin!'" Promising to reveal everything, "an evening with The Hoff" is "very, very intimate. Absolutely nothing's censored."

He's "excited", having visited the city before to judge the auditions of Britain's Got Talent and to see his friend, Radio 1 DJ Scott Mills host the Fun and Filth Cabaret last year. And although he won't be allowed to perform atop Edinburgh Castle, he still loves the Festival, despite being unsure what to expect. "I've had mixed reviews," the Baywatch and Knight Rider star reflects. "Some say it's going to be a drunk, crazy, fun audience. But I thought I'd been hired for a more sophisticated, West End-style show. Either way, I'm prepared."

His last show was attended by countless Germans and he indulged them with his greatest hits.

"We ended up bringing up a Berlin Wall, tearing it down, knocking it into the audience, everyone on stage dancing a limbo, then singing Delilah. They loved it," he enthuses. "The only bad review I got was for dressing up as Hitler."

He clarifies: "I'd been Hitler in a Las Vegas production of The Producers. Some people took it out of context."

Just turned 60 and a strapping 6ft 4in, Hasselhoff looks fantastic in the flesh, ridiculously so in fact, something he attributes to "drinking plenty of water". Tanned and with fiercely piercing eyes, in a green T-shirt and tight grey jeans that could embarrass a man half his age, he's quintessentially The Hoff, given to inexplicably raising his voice and referring to himself in the third person.

Where The Hoff finishes and David Hasselhoff begins is certainly difficult to ascertain. You'd be foolish to think it's the threshold of his penthouse in a London hotel, overlooking the Houses of Parliament.

Sequestered inside with his nephew and personal assistant Nick, monitoring online football odds "because there isn't much else to do", he enjoys the beautiful game enough to know Franz Beckenbauer personally, and that "Zoltan [Zlatan Ibrahimovic] is a diva". Last night he made and broke "a deal with God that if I won, I wouldn't bet for eight weeks."

As television's most watched performer in history according to the Guinness Book of Records, he can't venture outside without being mobbed and reckons he "can shut down Times Square in 28 seconds". Nomadic tribes in Kenya are ignorant of his existence but "the Maasai working in the hotel recognised me". A recent personal appearance in Hertfordshire pocketed him £12,000 simply for singing Jump In My Car, before "they played the Baywatch theme and all the girls took off their tops". "It's just so tiring and stupid," he shrugs, leaning back across a sofa. "You feel like Santa Claus".

Indeed. So ubiquitous and diffusive is the perma-grinning Hoff brand, endorsing everything from an Avatar-themed nightclub in South Africa to a German microwaveable sandwich, that notwithstanding the latter turn as ultra-camp, Teutonic snack-pusher Gunter "Mr Lean" Hasselhoff, the only screen roles he gets sent are self-caricaturing cameos. A shame, because he's a decent mimic.

Playing superhero Nick Fury in a TV movie last year, he was frustrated to be overlooked for The Avengers blockbuster in favour of Samuel L. Jackson. "I don't have the right representation to get me into those circles," he sighs. His manager naively believed he'd "never work again" after recent schlock-horror Piranha 3DD, in which he delivered a savage self-skewering, a celebrity lifeguard at the opening of a killer fish-infested swimming pool.

Yet he signed up for the ludicrous "blood, tits and ass" fest for leverage with producer Bob Weinstein's brother Harvey, who owns Knight Rider's rights. Weinstein reportedly plans to reboot the 30-year-old series as a movie, bringing Hasselhoff back as Michael Knight, the father of a new hero of the road. Only this week, the actor suggested at San Diego's Comic Con convention that this could happen sooner rather than later.

Before all that, there's a big screen version of Baywatch. Yet instead of reprising his "hunk in trunks" Mitch Buchannon, Hasselhoff will once again be playing himself. As the television series's executive producer, he was behind the revival and global syndication of the marathon show after NBC canned it in 1989. Over nine more seasons, it became the most successful ever, making him incredibly rich. A significant male demographic never tired of seeing nubile girls in red swimsuits.

"At some conventions perhaps," he shakes his head. "Never at colleges though, woah!"

History doesn't relate whether Chancellor Helmut Kohl and his East German counterpart, Erich Honecker, were committed viewers, before they consented to Hasselhoff belting out Looking For Freedom on a semi-demolished Berlin Wall on New Year's Eve, 1989, wearing a Knight Rider jacket with red flashing lights. Only that he gave them an ultimatum: on top of the wall or nothing. "I did say that," he admits. "But of course I would have done it anyway."

Bill Clinton, though, is a bona fide fan. In the Oval Office, Hasselhoff recalls the "nice guy" former President flirting outrageously with his ex-wife and erstwhile co-star Pamela Bach, "almost like a caricature of himself.

"If I'd only known (in their acrimonious 2006 divorce, when he took custody of their two daughters, Bach accused Hasselhoff of violence, a charge he always denied). I'd have been 'take her, take her, please get her out of my life, call her Monica, I don't give a damn'. My biggest mistake was not leaving her."

Despite rejecting narcotics while at the liberal California Institute of the Arts, where public nudity was embraced at Halloween and it was "very dangerous, a university of drugs, I was always in theatre while everyone else was taking LSD and jumping out of windows", the actor has long battled alcoholism, entering the Betty Ford clinic.

In 2007, a video appeared online showing him drunkenly struggling to eat a cheeseburger on the floor of a Las Vegas hotel room, while his daughter Taylor Ann begged him to curb his drinking. At the time, he claimed it was "deliberately released" but now maintains it was stolen from her camera.

Philosophical about a once-friendly media that turned "abusive and disrespectful of my children - it took a toll on me emotionally", he still "secretly" manages his daughters' group, The Hoff Drops, after launching them in the short-lived reality series, The Hasselhoffs. He's advised them "they're going to run into a lot of crap". But "if anyone says anything bad about me, they're in your face."

Beginning preparations for Hoff Broadway shortly, a "very funny, irreverent" New York musical penned by a team from the comedy show Saturday Night Live, he's also releasing an album of country pop.

"I had the music sent a while back but I just wasn't ready," he explains. "I was in the wrong place, going through the divorce, trying to get out of the whole drama dance, get out of the ring, don't engage.

"Everyone in a relationship that's not working, don't engage because you can get addicted to shouting at each other. Just walk. Don't let that weird stuff rent your head. When love comes you need to be open." Despite his tongue-in-cheek motto of "don't hassle The Hoff" and Nick's alertness – "he's really quick to grab the camera, take the picture and we move on" – he met girlfriend Hayley Roberts in Cardiff after she asked for a snap. Subsequent trips to Welsh pubs have been "like being attacked by friendly pirates".

He still chats with fellow BGT panellist Piers Morgan but not Simon Cowell, "he's too busy". Familiar with both sides of the judging process, as a talent arbiter and as the first celebrity eliminated from last year's US series Dancing With The Stars, he's decidedly ambivalent about the genre. "They're wonderful stories that make a lot of money for the producers," he says carefully. "It's great to have the ambition to be on them but they're not 100% honest, the motive is always ratings. Yet even when they lose, as long as no-one gets their feeling hurt, it's a tremendous showcase. In Vegas this year, half the people I knew from America's Got Talent were there."

He won't be surrendering his own fame without a fight, despite the pressures, because "I've never bought a ticket for anything.

"I performed for a million people in Berlin two New Year's Eves ago and woke up the next morning in Australia. Frankly, my life is a giant cartoon. I have no idea where I'm going next. Or where I am. I roll with the punches."

An Evening with The Hoff is at the Pleasance Grand on the Edinburgh Festival Fringe form Tuesday August 21 to Monday August 27. www.pleasance.co.uk