In a strange boxy building off the Rue de Bercy, on the Right Bank of the Seine, there are two wildly different Dennis Hoppers on display. The first one, on the seventh-floor exhibition room of this Frank Gehry-designed Cinémathèque Française, is a monumental icon of creativity. From all five rooms of a painstakingly researched show entitled Dennis Hopper et le Nouvel Hollywood, he glares out at you, with those trademark flinty eyes, in gorgeous monochrome portraits from artists as diverse as the sculptor George Herms, the actor Roddy McDowall, and the celebrity snapper Annie Leibovitz. This Hopper is the one in the show's centrepiece Warhol screen print looking angelic in a cowboy hat. He's also the one behind the many deftly taken photographs of famous artistic and Hollywood peers that litter the exhibition, and he is the one who did the Rothko-inspired yellow canvas in the corner, the zany pop-art “bomb-dropper” sculpture in the middle, and the torn-up Lucio Fontana-esque painting on the side. He is, in other words, and according to the curator Matthieu Orléan, “a Hollywood icon, a standard bearer for youth and non-conformism, and a symbol of liberation."

The other Dennis Hopper, however, the one sitting in a glass antechamber on the ground floor of the Cinémathèque, pensively fiddling with a cigar stub, is a different story. If not quite a vision of Yeats's “tattered coat upon a stick”, he is, today at least, wearing his 72 years with a certain sombre sadness. Normally an interviewer's dream, dishing out laughter-ridden anecdotes about orgies with Natalie Wood, and cocaine binges on the set of his 1971 flop The Last Movie, instead he is in a neat grey suit and open-necked white shirt, and soft white goatee, and quietly regretful about his past and his former self. He calls himself, for instance, a “f***ing idiot” several times, while his sentences occasionally drift off into disappointed silence. Mostly, though, he seems uncomfortable with his status as a creative success, when everywhere he looks he sees failure.

“I just thought I was dust in the pan until this came along,” he says, referring to his surprise lionisation in the floors above him. “I hadn't gone on to make the great movies that I thought I was going to make, and that I said I was going to make. So I'm not sure if I deserve the honour. It's way over my head. But I suppose I'll take it.” He forces out an attempted trademark manic Hopper giggle at the end, but his heart isn't in it.

He says for instance, that he is in some ways a photographer by default, and that even in the early days, as an 18-year-old from Kansas on contract to Warner Bros, it was always movies first. “I was really taking photographs because I thought I would eventually end up directing films,” he says, before explaining how the idea was sparked by his close friend and early mentor James Dean. “One day Dean saw me taking photographs and said: ‘Don't crop your frames, compose within the frame! You're going to want to make movies some day, and you can't crop film!”

Dean also introduced him to the guiding lights of the Pop Art scene in the 1950s. They went to an LA performance art “happening” together in 1954 where they met Wallace Berman, Edward Kienholz, Walter Hopps and Ed Ruscha. “Dean died a year later, and I just stayed on with that group,” he says. “Then I started photographing them, and did the early photographs of Andy Warhol and Jasper Johns before they were famous.”

And yet, he says, he was never really on the “inside” of that scene. “All those artists, they'd see me coming along with my camera around my neck and they'd say: ‘Hey, here comes the tourist!'.” He sighs for a moment. “It's funny, but the artists used to think of me as an actor, and the actors used to think of me as an artist. If every group you associate with thinks you're from the outside, that's what you become - an outsider.”

Hopper describes how his movie and artistic careers were tightly intertwined. When one flourished, such as the counter-culture classic Easy Rider that he directed, the other usually perished. He stopped taking photographs on the Easy Rider set and didn't start again until the 1980s, when his film work was nugatory. It wasn't just his well-documented antics (three grams of cocaine and 30 beers a day) on the set of The Last Movie that ruined everything, he says. It went deeper than that. “I spent my whole life looking at and admiring artists who drank and took drugs, like Baudelaire, Rimbaud and Verlaine,” he says, insisting that it was artists and not some flaw from his childhood (his war-veteran father was distant and unemotional, his mother unloving) that made him wild. “I was looking at these guys who were really abusers, and thinking, ‘It's OK for me to be like that, because I'm an artist. But I wasn't an artist. I was a f***ing idiot.”

He emerged in the mid-1980s clean and sober, with a formidable collection of classic American art (today he owns Warhols, Schnabels, Basquiats, Lichtensteins and Harings), but with a movie career in shreds. He was occasionally given handsome supporting roles in films such as Rumble Fish and River's Edge, but generally he was reduced to playing psychoheavies in a series of paycheque parts that he famously refers to as, “a long river of shit”. Naturally, his one true love, movie directing, lay beyond his grasp (“I was basically blackballed by the industry”).

It was during this period that he became a vocal Republican and Reaganite. Was this perhaps motivated by a sense of disgust at his younger libertarian self? “Not at all,” he says, calmly. “I became a Republican because I believed in Thomas Jefferson, who said that if one party has been in too long then they have to be replaced, so that democracy can function. The Democrats had been in too long back then, and right now I have to acknowledge that the Republicans have been in too long and it's time to go the other way, and to make Obama president.”

He says that in his personal life he's happier now than he's ever been. “I have four wonderful children, all from different mothers. I've been married five times and the wife I'm with now, Victoria [Duffy, a former actress], I've been with for 17 years. I went through a lot of stuff with women.” He pauses, his eyes glaze slightly, and you wonder if he's thinking about the eight-day marriage to Michelle Phillips from the Mamas and the Papas, or the accusations of spousal abuse that brought it to a close. “I was the type of guy, if they were with me for some time, who'd have to get rid of them or marry them. Which may not have been the smartest thing in the world.”

He adds that professionally he's still unfulfilled. He's taking photographs every day and he's just finished a high-profile 13-part TV series, Crash (adapted from the Oscar-winning movie), in which he plays a Phil Spector-type drug-crazed music mogul who kicks the habit. “It's the best role I've had in my entire career,” he says, deadpan. And yet. “I still haven't directed the great movie I wanted to. I haven't directed in 16 years, but I've been trying to, every single year,” he says, colour rising. “And then I start thinking about Orson Welles and all these f***ing people who, at the end of their careers, wanted to get movies made but couldn't!”

He lifts his head back and looks up to the ceiling, perhaps praying for guidance from the super-creative Dennis Hopper six floors above him. And then he shakes his head. “It's so f***ing sad, man.”

Dennis Hopper et le Nouvel Hollywood, Cinémathèque Francaise, 51 Rue de Bercy, 75012 Paris (www.cinematheque.fr 0033-1- 71193333), opens today until Jan 19

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