A college drop-out, Sam Shepard became involved in fringe theatre and won plaudits for his high-octane plays. Rock 'n' roll, drugs and the explosive tensions of life on the American edge are his themes and he has been hailed as the cowboy laureate, while as a Hollywood actor he has been compared to Gary Cooper.

In Rolling Thunder Logbook (1977), his chronicle of Bob Dylan's 1975 US tour, Sam Shepard writes: "Myth is a powerful medium because it talks to the emotions and not the head. It moves us into an area of mystery ..."

As he completes the 40-mile journey from his Minnesota ranch to the city of St Paul for a rare interview, these same observations seem applicable to Shepard himself. Throughout his career, he has been adept at creating mythic personae: the cowboy playwright, the occasional rock star, the smouldering all-American movie hero. And in the bland, mid-western urban sprawl of St Paul, Shepard's iconic presence is thrown into starker relief.

He's incongruously dressed in the uniform of the authentic Californian ranch-hand: blue jeans, cowboy boots and tan suede waist-coat. He drives a white Chevy pick-up so gigantic that it seems to roll down the streets like a stagecoach. Once parked, he dismounts with a calculated sweep, as if slipping from the saddle of one of his favoured quarter-horses. Installed in a booth at the St Paul Grill, Shepard reveals that he had been to a Dylan concert in the local stadium the night before.

"He is an extraordinarily beautiful writer of melody, but he is not afraid to really mess things up. Like for instance 'Girl of the North Country', which he obliterated in this concert. He's not afraid to take it some place else. He is absolutely courageous."

He goes on to describe how he has spent the morning working on his ranch.

"I keep endlessly busy with all kinds of stuff, mostly horses, cattle, livestock, things like that," he continues, "I've been into horses as far back as I can remember. There is a particular kind here in America called the 'quarter horse' that I'm very interested in." Here he gallops with his fingers-tips across the table to illustrate the unique mobility of this breed; the horse can spin through 360 degrees. "They came out of the southwest and were specifically designed to work with cattle. These horses work like cats."

He has chosen the restaurant, where the decor features a mahogany bear sucking on a huge cheroot, because of its authentic frontier cuisine.

"They do a great buffalo steak here," he says, in his buoyant western drawl, "it's the tenderest meat you ever tasted in your life ..."

The Sam Shepard mythology is built on an extraordinarily versatile talent, spanning an array of performance and literary genres. It is as a film actor that his persona has become known to a wider public, first as the rugged young farmer in Terrence Malick's Days of Heaven (1978) and later as the maverick test pilot in The Right Stuff (1983), for which he was nominated for the best supporting actor Oscar in 1984; the mysterious, laconic Faber in Volker Schlöndorff's underrated Voyager (1991) and, more recently, as the gruff commander in Ridley Scott's Black Hawk Down (2001).

At 59, with searing blue eyes and classic jaw line, Shepard is still a startlingly good looking man. Perhaps the real secret of his appeal, though, are the flaws: the gnarly teeth and the dangerous edge to his otherwise genial manner. His achievements in other fields will prove more enduring. As a screenwriter, he has been responsible for one of cinema's undisputed classics, Wim Wenders' Paris, Texas (1984). As a writer of prose he has ranged from the beguiling fragments of Motel Chronicles (1982) and the raw autobiography of Cruising Paradise (1996), to the short-story collection Great Dream of Heaven, published in November 2002 to highly favourable reviews. But it is as a Pulitzer-prizewinning playwright that Shepard's contribution has been most significant, leading the New York Times to hail him as the "playwright laureate of the west, consistently, ruthlessly true to his experience of a wilderness where American has always hidden its promise and its dream". Arguably his greatest achievement is the so-called "Family Trilogy" of plays: Curse of the Starving Class (1976), Buried Child, which won a Pulitzer in 1979, and the explosive fraternal confrontations of True West (1980).

"There is nobody else who writes his kind of dialogue," says Wenders, "And nobody touches these subjects, either. He makes a whole different kind of 'America' visible behind the obvious, contemporary one."

Samuel Shepard Rogers III, called Steve Rogers during his early years, was born on November 5, 1943 in the military outpost of Fort Sheridan, Illinois. His father, Samuel Rogers VII, was an officer in the Army Air Corps, stationed in Italy when Shepard was born, then afterwards in South Dakota, Utah, California, the Pacific island of Guam and the Philippines. Even when the family settled in the small Californian town of Duarte, there was little in the way of stability. Samuel Sr, according to Shepard, "a drinking man, a dedicated alcoholic", was confrontational.

"My father had a real short fuse," Shepard says. "He had a tough life - had to support his mother and brother at a very young age when his dad's farm collapsed. You could see his suffering, his terrible suffering, living a life that was disappointing and looking for another one. My father was full of terrifying anger."

Shepard has two younger sisters, Sandy and Roxanne. According to Roxanne, the tensions between father and son often boiled over.

"There was always this kind of facing off between them, and it was Sam who got the bad end of that. Dad was a tricky character, because he was a charismatic guy when he wanted to be. And at the other side he was like a snapping turtle. With him and Sam it was that male thing. You put two virile men in a room and they're going to test each other."

As a teenager, Shepard gravitated towards rugged, outdoor pursuits - rodeos and race tracks. Two semesters into his course in animal husbandry at Mount San Antonio Junior College in Walnut, California, he experienced a revelation.

"I happened to get into a literature class, I don't know how exactly," he says, "with a lot of guys from that area whom I had never had any contact with; for lack of a better word they were beatniks. They lived in this big old house and one of them was a painter and they were smoking a lot of dope out there, and they had stuff lying around like Beckett plays, Jackson Pollock reproductions, which I'd never heard of. That was the first encounter I had with Beckett, with jazz, abstract expressionism. And then I just left [college]."

Answering an advertisement in a local newspaper, he went along for an audition for the Bishop's Company Repertory Players.

"We did little short plays, adaptations of literature mostly and we did them in churches. It amazed me that you could just get a bunch of people together and write some stuff and do it and get an audience. People would actually come and see it. From nothing, you could make something brand new."

During one of the company's stop-overs in New York, Shepard decided to stay, and looked up an old high-school friend from Duarte, Charles Mingus III, son of the jazz legend.

"Sam said he needed an apartment," remembers Mingus, "and I said 'I got this apartment, the rent is a little steep, 60 bucks. Let's split it, at least it will save you from being on the street'."

Mingus also found Shepard a job as a bus boy at the Village Gate, the well-known Bleecker St jazz club.

"I was suddenly witness to the greatest jazz players of that era," says Shepard. "One night Cannonball Adderley, Thelonious Monk and Gerry Mulligan were playing and the relief comedian was Woody Allen."

At the Village Gate, Shepard found himself at the centre of the off-off-Broadway phenomenon that was seeing the emergence of experimental, underground venues such as Caffe Cino and La Mama. Influenced by Beckett and Pirandello, Shepard began writing plays.

"The head waiter was a guy named Ralph Cook who was trying to open a theatre at St Marks in the Bowery - it was called Theatre Genesis. He was gathering actors. A lot of the waiters were actors and he said I hear you are writing some plays and I said 'yeah', so I showed him a couple and he said 'let's do them' - just like that - and a week later we were doing them."

The first, Cowboys, whose author now styled himself Sam Shepard for the first time, baffled critics. "It owes debts to such unlikely parentage as Waiting for Godot crossed with Of Mice and Men," remarked the New York Post. Poor reviews and sparse houses notwithstanding, Shepard was soon being hailed by the New York Times as "the generally acknowledged 'genius' of the [off-off-Broadway] circuit".

Over the course of 1964-65, he produced a succession of chaotic, high-octane pieces, including The Rock Garden , an elongated domestic scene, The 4-H club , based on life in the flat he shared with Mingus, and Chicago , which was set in a bathroom and written, according to Shepard, in just one frenzied day. These works were often little more than drug-fuelled visions, incomplete and frequently incomprehensible but always with an undertow of brilliance.

"Sam was always taking chances, always being original," says playwright Edward Albee. "He was just one of the most exciting individual talents, somebody who was willing to fail and fail interestingly. And if you are willing to fail interestingly, you tend to succeed interestingly."

In 1967, Shepard wrote his first full-length play, La Turista, centering on an unfortunate vacation in Mexico during which he and his then girlfriend, the actor Joyce Aaron, were holed up in "a tiny sweltering motel room in the Yucatan", stricken by "a semidelirious state of severe dysentery". After a two-year break from the theatre, during which he co-wrote Zabriskie Point (1970) for film director Michelangelo Antonioni and toured as drummer with the cult "amphetamine rock band" the Holy Modal Rounders, Shepard returned, in 1969, with the The Unseen Hand, a rock opera about cowboy drifters.

During this period, Shepard's personal life underwent upheavals. In 1967, among the company of actors at Theatre Genesis, he encountered a pretty, baby-faced actress named O-Lan Johnson, then just 17. The first indication of Shepard's interest came when she auditioned for a part in his play Forensic and the Navigators (1967) only to find it contained a role called Oolan, whose character mirrored her own. A relationship soon developed, and with O-Lan conspicuously pregnant, the two were married in St Mark's Church in the Bowery on November 9 1969. The following May their son Jesse was born, named after Jesse James.

No sooner had Shepard become a father, however, than he embarked on what is perhaps his most infamous liaison, with the poet and musician Patti Smith. Their nine-month affair was intense and destructive, but it also produced Cowboy Mouth (1971), an absurdist theatre piece based largely in the room in New York's Chelsea Hotel where it was composed.

"I'd never written a play with somebody before and we literally shoved the typewriter back and forth across the table. We wrote the whole thing like that, in two nights," says Shepard.

The affair also appears to have been remarkably open, with O-Lan apparently happy to play a part in Shepard's play The Mad Dog Blues (1971) that was based on Smith.

"Me and his wife still even liked each other," Smith says, "I mean, it wasn't like committing adultery in the suburbs or something."

By now, however, almost a decade of excess, compounded by matrimonial discord and fatherhood, was beginning to take its toll on Shepard, and, after failing to turn up for the opening night of Cowboy Mouth , he fled with his family to London.

"I was into a lot of drugs," he told Time Out shortly after his arrival. "It became very difficult, you know, everything seemed sort of shattering. I didn't feel like going back to California, so I thought I'd come here."

Shepard spent much of his time in England, according to actor Tony Milner, betting at dog-tracks and racecourses. He also submitted his recently completed The Tooth of Crime , a surreal, freeflowing reflection on American pop culture featuring a strutting rock-star named Hoss, for production at Charles Marowitz's Open Space theatre in London (it premiered on July 17, 1972), and a new piece called Geography of a Horse Dreamer, for the Royal Court. It opened on February 21, 1974 with Stephen Rea and Bob Hoskins. Shepard was the director. However, Shepard soon became disil lusioned with London.

"Not long before he left, he said to me that the critics didn't want to know about his work," says Milner, "but I think that the problem was that it just went over their heads. You had critics like Harold Hobson, all quite old chaps. And he's talking about streetwise America and rock 'n roll and drugs - they didn't know what he was on about."

On his return to the US, Shepard settled with his family in Mill Valley, California, moving into a 20-acre ranch called the Flying Y. It was in this rural setting that his work began to undergo a revolution.

"It suddenly occurred to me that I was mainly avoiding a territory that I needed to investigate, which was the family. I was a little afraid of it, particularly in relation to my old man and all of that emotion. I didn't really want to tiptoe in there and then I said 'well, maybe I better'."

Curse of the Starving Classes ( 1978 ), the first work fully to reflect this shift and the opening part of his "Family Trilogy", took a more conventional three-act structure and infused it with the Beckettian immediacy of the early plays to form what the New York Times, in a review of the New York premiere in 1978 at the Joseph Papp Public Theatre, called a "style that oscillates between realism and savage fantasy". Shepard followed this up with Buried Child (1979), a drama about a family destroyed by the secret inferred in the title.

"This is the best Shepard play I have seen in some time," wrote John Simon in New York magazine, in one of a crop of overwhelmingly favourable reviews. "It is powerful obsessive stuff, intensely theatrical, not always disciplined but always wildly poetic, full of stage images and utterances replete with insidious suggestiveness."

On April 16 1979, Shepard received a telegram at the Flying Y congratulating him on winning the Pulitzer Prize.

"The weird thing was that the producers, for some reason or other, decided to close it that same day," he recalls. "You get this sort of medallion and then the play closes. I couldn't figure that one out."

But when, in 1978, Terrence Malick's Days of Heaven, in which Shepard co-starred, was released to ecstatic reviews, overnight the playwright was transformed into a top Hollywood name, much to his own initial horror.

"I had all kinds of wild offers at that time to be a movie star and I panicked. I was turning down things like Warren Beatty's Reds , that part of Eugene O'Neill [played by Jack Nicholson]. My agent was going crazy. I hadn't realised what the experience of it would be like - to be on the verge of being a movie star. Because it's like you are the hottest whore in town. Everybody wants you."

Shepard's first stage foray after winning the Pulitzer, True West ( 1980 ), a tale of raging fraternal rivalry, did little to allay these worries. Against Shepard's wishes, Joseph Papp insisted that the parts for the Broadway production in 1980 were entrusted to upcoming stars Tommy Lee Jones and Peter Boyle. From a film-set in Texas, Shepard blasted: "I would like it to be known that the 'production' of my play True West at the Public Theatre is in no way a representation of my intentions." The play might have been forgotten had it not been for the Steppenwolf Theatre Company in Chicago , which revived it in 1982 in a production with John Malkovich, directed by Gary Sinise: " True West , revivified, should now take its ightful place in the company of the best of Shepard," concluded the New York Times.

After True West, Shepard produced two other important plays, Fool For Love (1982) a claustrophobic trailer-trash love story which Jack Kroll of Newsweek decreed "a classic rattlesnake riff by Shepard" and A Lie of the Mind (1985) which won the New York Drama Critics Circle award for best play but which some critics felt betrayed early signs of creative exhaustion. Around this time, Shepard's personal life went through another upheaval, after he met actress Jessica Lange on the set of the film Francis (1982).

"I'd seen Sam in Resurrection [1980] and there was something about him that struck such a familiar chord," she recalls. "I immediately felt I knew something about him, that wildness, that typically American wildness, a no-restraints outlaw quality."

At the time, Shepard was still married to O-Lan and Lange was involved with Mikhail Baryshnikov. The relationship got off to a volatile start.

Lange says. "When we were together we were so wild - drinking, getting into fights, walking down the freeway trying to get away - I mean, just really wild stuff. I didn't want to keep going in that direction. So we quit talking. Then, through the work of some good friends, we got back in touch and that was it. He left his wife and we drove to New Mexico; and that's where we settled."

According to Lange: "He's a great man, a natural man, which is rare. I've known a lot of men. And you know I've had romances with what you'd call famous men, and none compares to Sam in terms of maleness."

He also has a reputation for straight-talking and a disregard for protective social niceties.

"Here is a man who could see right through you," says Wenders, "who would smell bullshit from a mile. He'd rather hurt you than be dishonest. There is no front. He is just all true. With a dissecting sense of humour."

By the late 1980s, Shepard was beginning to retreat from theatre, as his star began to wane.

"Though there are moments in Lie of the Mind [1985] [which won the New York Drama Critics Circle Award for Best Play, 1986] that are as powerful evocative and touching as anything he's ever written," wrote the San Francisco Chronicle. "The play as a whole seems to come from a seam that has been overmined by the playwright. At times, the script even approaches the outskirts of self-parody."

At the same time his increasingly high profile as a film star was beginning to raise uncomfortable questions.

"Once a mysterious presence behind a wealth of cryptic plays," commented Robert Brustein in the New Republic in 1996, "today he finds himself a highly publicised celebrity, not through his theatre work, which never managed to draw a mainstream public, but largely as a result of his screen appearances, beginning with The Right Stuff, which brought him momentary fame as the new Gary Cooper. Shepard's movie roles have been occasional, even desultory lately, and the once prolific dramatist has only produced three plays in over a decade." Shepard was terrified that his status as film star would compromise his reputation as a playwright.

"There was this feeling that my credibility as a writer would go in the toilet if I suddenly became Robert Redford. I didn't want to be a movie star. I didn't want to have that thing of being an icon. It scared the shit out of me." He now admits, however, that he has grown inured to the condition: "It's like having a little oil well back there in the backyard - you go and dip into it," he grins.

In the end, it wasn't Shepard's burgeoning celebrity but his unwillingness to repeat himself that led to an inevitable reduction of theatrical output. Both States of Shock, premiered in 1991, a response to the Gulf war that echoed his early work, and the uneven Simpatico (1994), a play reminiscent of David Mamet in its partially submerged narrative, were not particularly well received. And When the World was Green , his 1996 collaboration with the late Joseph Chaikin, which has just completed a run at the Young Vic, led critics to suspect that Shepard's light touch with mythology had faltered.

"It is a basic rule of drama that mythic meanings grow from concrete situations," wrote Michael Billington for this paper, "but here you feel Chaikin and Shepard have started with universal ideas about revenge and rebirth and invented a story to illustrate them."

Calls from reviewers for a return to the familiar Shepard territory of the "Family Trilogy" have gone unheeded. And producers must content themselves with revivals from his back-catalogue, such as the forthcoming new production of True West at the Bristol Old Vic. Shepard is working on more stories and a new screenplay with Wenders but there are no concrete plans for further new plays.

"At the moment my ambition is to ride some good horses," he says with a chuckle, "I would still like to keep my hand in the acting deal, as a character actor or in some way shape or form. And writing wise, I'd like to keep all the doors open. I would love to do another play, but I am waiting until I encounter some material that is new. I don't want to write the same shit over and over. I suppose that the danger is that you can wait too long. But hopefully there is something out there."