Brian Cox is a ball. If I didn't know better, I'd say he's just rolled his way to my table. His donkey jacket is hunched around his shoulders, his head is tucked in, his stocky body is the same size in every direction. His stubby fingers are made of the same amorphous lump of clay as his face, which today has a light grey moustache and a thinning crop of slicked-back grey hair. He has curled himself up like a hedgehog.
As he sits down, his mind is elsewhere: back in the rehearsal room for Uncle Varick, a new version of Chekhov's Uncle Vanya shifted from provincial Russia to the remote north-east of Scotland. Written by John Byrne, playwright, artist and husband of Tilda Swinton, it is set in the era of The Beatles' Rubber Soul, but in a place where the Sixties have yet to swing. Cox thinks it's the best translation of the play he's ever read, and in some ways even better realised than the original.
But the actor, who is leading the Edinburgh Royal Lyceum company, is suffering from a form of culture shock. The man who played King Lear at the National and Titus Andronicus at the RSC hasn't been near a stage since he starred in Conor McPherson's Dublin Carol in London four years ago. Instead, he's been working his way through Hollywood, playing pretty much any part that would come his way. "I've done some shite films, but I've also done some very good ones," he says, counting LIE, 25th Hour and Adaptation among his better choices.
His output has indeed been phenomenal - 20 films since 2000, with at least five more due for release - which is why he's finding it hard to stop thinking like a movie star. "I don't think of myself as a theatre animal any more," he says. "In movies, you come in, do your stuff and get out. It's up to the director to put it together. But when you're acting in something like this, you've got to have a sense of orchestration and rhythm." So four days into rehearsals, the Dundee-born actor is reacquainting himself with the joined-up thinking required of the stage. "I'm not feeling very intelligent," he says, taking off his glasses to rub the tiredness from his face.
But as he limbers into conversation, Cox gradually uncoils himself from his ball of introspection. By the time we're through and he's running late to get back to rehearsals, he has physically grown before me, his arms all expansive gestures, his head tilted high, his pure blue eyes holding contact. And, despite his protestations, he's as intelligent as ever. Cox has that rare combination of being not only restless, emotional and instinctive, as so many actors are, but also bright, articulate and opinionated, intellectual qualities not always treasured by his profession.
"You have to learn to use your brain," he says. "You have to learn the finite nature of the material you're working with. You have to make the right choices for a combination of intellectual and emotional reasons. If actors aren't smart enough, if they don't have a sense of who they are and what they do, they get stuck. Actors who are very flexible and eminently watchable usually have a good thinking ability: people like Duvall and Hackman - and the great example is Bill Murray." Is the combination of instinct and intellect one that gets him into trouble? "Yes," he says. "Because they don't understand that. They think you're coming from one place, then they find you're coming from somewhere else." He doesn't say who "they" are, but it's fair to assume that Cox is always coming from somewhere else. "My career hasn't followed the usual path," he admits. "It's always had its own life."
Cox, 57, is always busy with something. Correction - he's always busy with several things at once: "It's my Gemini nature," he says. As if it wasn't enough to tour the world for a year in Deborah Warner's King Lear in 1990, with a smaller part in Richard III on his nights off, he found time to write a book about his experience (The Lear Diaries). Yet, ever capricious, he found himself rebelling against the institutionalism of the National and moved on again. "I'm not attached," he says. "It could all go away tomorrow. I've always lived like that." Instead, he switched his focus to TV and film. He'd already played the first Hannibal Lecter in Manhunter in 1986 (five years before Silence of the Lambs and an interpretation many think superior) and consolidated his screen reputation in films such as Ken Loach's Hidden Agenda. Now he's hot property. In the past year alone, his filming schedule has taken him to Vancouver (X-Men 2), London (The Bourne Supremacy), Texas (The Ringer) and a hurricane-blasted Mexico (Troy).
Meanwhile the acting career of his 35-year-old wife, German-born Nicole Ansari, has drawn him to Venice, and elsewhere in Europe, from their theoretical home in Los Angeles. In the middle of all this they are due to have a second child at the end of October. Typically, Cox has yet more schemes and commitments on the go: after he was diagnosed with diabetes five years ago, he ended up as a spokesperson for the Diabetic Research Centre in Dundee, and on the odd day when he's not in front of a camera, he's nurturing plans to direct a film about Elizabeth Barrett Browning.
The next British audiences will see of his frenetic activity is his role as Agamemnon in Troy, Wolfgang Petersen's retelling of Greek legend starring Brad Pitt, Orlando Bloom and Saffron Burrows. "I've moved up the ladder as far as films are concerned," says Cox. "Agamemnon is wonderful. He's like a juggernaut: once he starts moving, the assault on Troy doesn't stop." Troy is the kind of film they don't make any more: a grandiose historical epic like, for example, Lawrence of Arabia. And who should be playing Priam, King of Troy, but TE Lawrence himself? "Peter O'Toole is like an icon to me," says Cox. "I'd never met him before and I was very nervous, and on my first day I had to kill him. My first day and I'm killing Peter O'Toole!"
Next, in The Bourne Supremacy, he's reviving the part he played opposite Matt Damon in The Bourne Identity. "Ward Abbott, who was quite secretive in the first film, emerges as an extraordinary character," he says. "It's on the level of a Hackman role. I've also been exercising my comic ability in a Farrelly brothers film called The Ringer. The range is beginning to open up." The globe-hopping involved in all this has given Cox a perspective that straddles the Atlantic. He's able to talk as knowledgably about British politics as North American, being at once distant and part of the two communities. He was sitting on the runway at Kennedy airport when al-Qa'ida hit the twin towers ("It looked like an effect from Universal Studios") and watched how the USA came to terms with the attack. "They were like a child who had been smacked and didn't know why," he says. "They kept saying: 'But I'm good!'" He views Bush and Blair as characters out of Greek tragedy. "It's all about their fathers," he says. "It's like Mel Gibson in The Passion...: it's not about Jesus Christ, it's about his dad. With Bush, it's about proving himself to his father: 'I'm doing something that my father couldn't do and avenging my father at the same time.' With Blair, it's also to do with some version of his own high Anglican Christianity." The Prime Minister, he feels, is "patronising without being paternal" unlike, say Lord Reith, who was "patronising but a great dad". Fatherhood, it seems, is on Cox's mind. He has two grown-up children, Margaret and Alan, also an actor, from his first marriage, and now his youngest son, Orson (named because he looked like a little bear, not because of Orson Welles), is about to gain a sibling.
Cox, the youngest of five children brought up in a poor Irish-Catholic family, was just nine when his own father died. How did that affect him? "His death has formed everything about me," he says. "But it's been more of a blessing than a curse because I haven't got Mel Gibson's or George Bush's problem. I have to honour his spirit, but I don't have him breathing down my neck saying: 'It's gotta be like this.' I had to stand on my own two feet, probably a little too early - earlier than most people. I probably lost quite an important part of my childhood. But it's swings and roundabouts. Apart from the regret of losing your daddy - and that was awful, really excruciatingly painful and the memory of the pain still is - I'm very blessed because I don't carry the sins of the father around with me." Might it explain his restless nature? Has it created something unresolved in him? "I don't think I'm unresolved," he says. "I think I'm a quester. Life is about a journey, I don't think it's about standing back. I envy friends of mine who have retired and they're living in the south of France and their day is spent in a wonderful Zen-like way. I'm agog at that, but it's not me. I can't do it. They have an inner peace and I'll come to that, but I have to do it in my own way. I'll probably come to it when the legs have given way and I can't move any more."
'Uncle Varick': Royal Lyceum, Edinburgh (0131 248 4848), 16 April to 8 May. 'Troy' is released on 21 May and 'The Bourne Supremacy' on 13 August