Dennis Hopper is recreating his famous role as a wild biker in an ad for the Ford Cougar. Jason Barlow was the only reporter allowed on set to meet him
The man who accidentally detonated Hollywood, who became more of a raging bull the further away he got from Easy Rider, is sitting patiently on a windy Californian mountain. There is no sign of the demonically supercharged laugh that has lifted many of his best films, even in the midst of the fluttering ministrations of a make-up person.

And while Dennis Hopper once claimed to have personally introduced cocaine to the streets of America, these days herbal tea is as far as he's prepared to push the boat out. Like so many other retired hellraisers, he no longer even smokes.

Hopper's sober reformation is signalled by his involvement in the television ad for Ford's new Cougar coupe, which has just gone on sale in the UK. And while many superstars simply sign up for lucrative adverts in a desperate act of creative bankruptcy, the 60-second Cougar commercial is an unusually witty and clever vehicle for a new, er, vehicle.

"Wild at heart, that was the starting point," says Leighton Ballett, one of the creatives at Young & Rubicam, the agency responsible for the campaign. "The Cougar is a car for people who once liked to race around but have grown up. We needed someone who had been like that, someone like, say, Dennis Hopper.

"Then we thought about Easy Rider and decided if we didn't ask we'd never know. You do things like this as a piece of magic and hope you get away with it."

As television ads for cars go, the Cougar Easy Driver film is magical, not least because Hopper agreed to do it, but also because it proved to be a massive technical challenge. Remember the Steve McQueen ad for the Ford Puma (the work of the same ad agency)? Well, that was a doddle in comparison, and its star was dead.

On set today, the crew is shooting film that will eventually blend seamlessly with footage lifted straight from an original print of Easy Rider; the seminal hippy biker movie Hopper made with Peter Fonda in 1969. The technical trickery extends to the presence of both a mobile editing suite and a special effects facility to ensure that camera angles and lighting are checked and perfected immediately.

Hopper, in effect, will be acting alongside his most demanding co-star ever - himself - and you simply will not see the join. Steppenwolf's hoary old classic "Born To Be Wild" has even been revved up once again for the soundtrack.

Hopper seems to be enjoying the process enormously. "Oh it's great. Paul Street, the director, is a master, and we're doing technical stuff that has never been attempted before.

"I'd like to work with Paul when he starts making feature films. It's great to look over your shoulder and see the young you there - it's like a dream."

Turns out he loves Fords too: "When I was a young man in Dodge City I was raised by my grandparents. They had wheat farms in Garden City so we had Ford trucks, we had Ford products, and we've used them all my life."

What about the legacy of Easy Rider? There's definitely a degree of self-parody here, isn't there?

"Well I'm very proud of it. It was the first film I wrote, directed and starred in. Through the years Peter [Fonda] and I have had a lot of fights over the picture, but we're all proud of it.

"The motorcycle represented the horse to me, it was like making a Western, stopping at campfires and strangers coming into town, you know they could take your wife and kids and run off with them."

Not exactly the sort of people that Ford believes will be buying its stylish new Cougar coupe, but that's pre-millennial marketing for you.

And menacing Dennis? Well a Ford Cougar would suit him just fine: "It's great. It's got a proper stick shift, five forward gears and is real comfortable."

Hellraising - it just isn't what it used to be.