Which is precisely how McGregor himself comes across, no matter how diverse the characters he has played in his crowded schedule of 10 films in four years. The most popular, and most celebrated, film star of his generation, he takes on unfeasible amounts of work, throws himself into wildly eclectic roles (from Emma to Star Wars), has taken on the stage with a play just starting at the Hampstead Theatre and through it all, has a high old time both on and off set. Despite being a famously doting family man, he is a legendary drinker, hell-raiser and party animal. He was nicknamed "Ewan McLigger" by The Mirror. He turns up in the inner sancta of Celebrity Nitelife - on the eve of the Scotland vs Brazil World Cup match, he was in the Paris bar where Stan Collymore thumped Ulrika Jonsson. Journalists love him because he gossips indiscreetly about fellow actors, and sounds off about the iniquities of the Hollywood "machine". At the Scottish People's Film Festival, after a screening of Trainspotting where they bleeped out offensive words, he accepted an award and said: "For those of you who missed it, the words were fuck, fuck, fucking, fuck and fuck." He revels in excess, getting stupendously drunk to a degree that makes his friend Liam Gallagher look like John Selwyn Gummer.
He is pure energy, the eternal yes, the uncontainable id, the go-for- it dreamer, the try-anything-once headcase.
In Trainspotting, his eyes shone with a mad light as he embraced destruction: "No thanks," he said, turning down the offer of preliminary drinks, "I'll just proceed directly to the intravenous injection of hard drugs...". In A Life Less Ordinary, he was the hopeless loser who kidnaps the feisty Cameron Diaz. And this week, he can be found in a cinema near you, going berserk on a rock'n'roll stage with his trousers round his ankles.
It is a scene that every viewer of Velvet Goldmine gleefully anticipates: the first sighting of Curt Wild, a demonic, hyperactive American rocker. Wild/McGregor is on stage, dealing with a hostile and heckling audience. He drops his silver jeans to moon at the crowd, waves his penis in their faces and bounces around like a madman. It is a display of ballistic egomania that almost eclipses the memory of Iggy Pop, the exhibitionist front man of the Stooges, on whom Curt Wild is clearly based.
"I was worried I wasn't going to make it through the number because I'm not very fit," he told Interview magazine this month, "but as soon as the camera started turning, I stopped worrying because this mad stuff started happening..." The fact that he was facing a crowd of actors rather than rock fans didn't bother him; he was in the Brixton Academy, on stage, getting his rocks off.
"It was great to be there at 4am in front of 400 extras, getting paid well for doing something that would normally end you up in prison," he told Time Out.
He was living out a fantasy. In his teens, he would routinely play Billy Idol's "Rebel Yell" at colossal volume before going to school in the morning. He grew up in Crieff, a small town in Perthshire, Scotland, and attended the grandly named Morrison's Academy, a private school where his father was the PE teacher; his mother was deputy head of a Dundee high school.
The burden of two magisterial parents gave the boisterous adolescent an attitude problem; he suffered from depression, and was hauled before the headmaster for antisocial behaviour. At 16 he left school, to general relief, and headed for Perth Repertory Theatre.
His ambition to be an actor was sealed by the age of nine. He attributes it to three things: his passion for black-and-white movies on television; his chronic adoration for every principal boy in every pantomime he attended; and the influence of his uncle, Dennis Lawson, the actor and singer best known for his starring role in Local Hero. Lawson used to visit his Perth relations, travelling up from London in his cool flares and Afghan coat, and bringing a whiff of green room glamour and metropolitan trendiness to McGregor's provincial backyard. Ewan left home, took a drama course at Kirkcaldy College of Technology, then headed for London, aged 17. His first film part was as an extra in A Passage to India, when, he said, "my life went into widescreen. I had a ball, and the depression lifted". In his final year at the Guildhall School of Speech and Drama, he got a breakthrough: a part in Dennis Potter's Lipstick on your Collar, in which he played a disaffected War Office clerk who fantasises about becoming Elvis, and shook a mean tail-feather in the rock'n'roll dream sequences. The part could have been written for him.
At 23, as Alex in Shallow Grave, he looked every inch the new star on the block - handsome, callow, devious and damnably sexy. At the end, when he is once again lying on the floor (it's a motif of the film) but with a huge kitchen knife skewering his arm to the lino, he manages a radiant grin that sums up all the actor's indomitable, unsinkable life force. It was a good year for him - 1994. He'd met Eve Mavrakis, a French set designer, on the set of Kavanagh QC, the legal-eagle television drama series. They were married in France a year later. "I completely believe I will be with her for ever," he says fervently, "and that we'll go through everything together. Otherwise I wouldn't be married." They now have a daughter, Clara, who will be three in February, and live in some luxury in Belsize Park, north London.
Shallow Grave was the first feature by the gifted troika of Danny Boyle (director), Andrew McDonald (producer) and John Hodge (writer). They were all together at the Sundance Film Festival, when they heard that Channel Four had agreed to co-finance Trainspotting, from Irvine Welsh's best- selling book. They gave McGregor the script to read, but without guaranteeing him the key role of Renton. "He was like a Christmas present," McGregor said of the part. "I'd been waiting for him to come along and when I read the script I thought, well, here he is - here he comes. For months beforehand, I thought about nothing else, and I threw myself into it 100 per cent and played him with a passion."
It was a curious kind of starring role - a skinny, crop-haired, pustular heroin junkie whose most sublime moment is diving head first into a crammed and reeking lavatory to rescue the opium suppositories he has just voided, and emerging in the blue, transcendent waters of druggy bliss. It was a squalid, vicious movie, desperately uncertain in tone, but it grabbed the mid-Nineties zeitgeist by the throat and shook it. McGregor's skinny, drenched image was on every bus, advertisement hoarding and magazine cover.
The Boyle-Hodge-McDonald team cast him in a third film, A Life Less Ordinary. They seemed to be a quartet that would last for ever, with McGregor for ever playing d'Artagnan to their Three Musketeers. But that moment of uncertainty at the Sundance Festival, when they wouldn't guarantee their star a part in Trainspotting, proved to be prescient. For their next feature, The Beach, based on Alex Garland's backpacker best-seller, they bypassed McGregor and offered the lead to Leonardo DiCaprio. It seems an extraordinary slap in the face to a lucrative colleague and friend, but McGregor is philosophical. "They needed more money and he's more bankable," he told Time Out. "There was no big falling-out, but I was hurt. I haven't seen Danny [Boyle] since."
He has not, of course, spent many nervous hours waiting by the telephone for a substitute project. There are about six McGregor films awaiting release. In Rogue Trader he plays Nick Leeson, the spendthrift dealer who brought down Barings bank. He plays a thick pigeon-fancier in Jim Cartwright's The Rise and Fall of Little Voice, with Jane Horrocks and Michael Caine, directed by Mark Herman who previously directed him in Brassed Off. More recently, he filmed Serpent's Kiss, about a 17th-century craftsman who falls for his employer's wife (Greta Scacchi), and flew to America to make Nightwatch with Patricia Arquette, playing a law student accused to being a serial killer. And he was signed up by the legendary George Lucas to play Obi Wan Kenobi in the "prequel" to Star Wars, Balance of the Force.
The only rip in this seamless robe of success concerns his family. In interviews, a querulous note sometimes sounds about the strain put on his domestic life by his inability to say no to anything. "Working on films back to back, I began to find I was losing myself... I'd completely forgotten what it was like to get up in the morning and sit and watch the telly. I didn't have a bath for two years because I didn't have a fucking tub." His feelings that he might be neglecting his family crystallised during a terrible period when his baby daughter Clara contracted meningitis and nearly died. As she was rushed into the casualty unit of the Chelsea and Westminster hospital, Ewan was in Los Angeles, guest-starring (ironically) in ER, guest-directed by Quentin Tarantino. He flew home in a panic and found Clara wired up to a heart machine. "Your daughter is doing well", the doctors told him. He pulled a photograph from his pocket. "This is what my daughter looks like when she is doing well," he tearfully informed them.
Clara was in hospital for nearly three weeks, but made a full recovery. McGregor was badly shaken by the experience. He has been through a period of emotional retrenchment this summer, turning down films, seeing his family, playing golf and preparing to go back to the theatre. From now to 2 January, he can be found on stage at the Hampstead Theatre, playing the title role in Little Malcolm and his Struggle Against the Eunuchs, by the Sixties one-hit wonder David Halliwell. It is directed by his Uncle Dennis, as if the born-again family man were determined to keep his professional life familial too. The spring will be devoted to his pet project of producing a film about Nora Barnacle, the Galway chambermaid who became James Joyce's earthy consort.
An exhaustingly energetic fellow, he has done more at 27 than most actors (and most drinkers) achieve in a lifetime. And he has scruples about quality. His stated reason for returning to the theatre, for the first time in five years, is fear of complacency. "I felt I was getting a bit lazy," he says. "I want to remember what it's like being really frightened again. The fear of being crap is always what makes you good, I think." And that is as near to discussing his "motivation" as Ewan McGregor is ever likely to get.
Origins: Born 31 March 1971, in Crieff, Scotland.
Family background: Father, Jim, a teacher at Crieff's Morrison's Academy; mother Carol, deputy head of King's Park High School in Dundee. His uncle, actor Denis Lawson. Brother, Colin, RAF pilot.
Vital statistics: Married, Eve (right), a French production designer, with daughter, Clara.
Training: Guildhall School of Music and Drama.
First role: Private Hopper in Dennis Potter's Lipstick on Your Collar on TV.
Films: 21, from Being Human (1993) to James Joyce in Nora, Nick Leeson in Rogue Trader and Star Wars, Episode 1.
Current role: Bisexual title role in a play, Little Velvet Malcolm and his Struggle Against the Blue Room Voice, co-starring Jane Horrocks.
On his influences: "Sex, my uncle, and black-and-white movies."