The face is long and lantern-jawed with a monastic fringe of silver hair. The outfit and stage setting—black suit, black T- shirt, black-draped rear wall—seem conceived as a defiant essay in Calvinist gloom, as if to say: "This may be the Cannes Film Festival, ladies and gentleman, but you are here to peer into the soul of art."

A picture tells a thousand words. But how do words do justice to an image we've seen a thousand times before—or certainly a hundred—and grown to love? Sweden's greatest living actor began as the face of Ingmar Bergman's cinema, then brought his gaunt majestic miserablism to English-speaking movieland. This side of the Baltic, Max Von Sydow has been Jesus and the Exorcist; a Bond villain and Ming the Merciless (Flash Gordon). He was sombrely hilarious as the voice of agnostic despair in Woody Allen's Hannah and Her Sisters ("If Jesus were alive today, he would throw up at the things said and done in his name."). On stage he was a daring, daunting Prospero for Jonathan Miller.

Now this Pope of lofty angst is giving an actor's masterclass. "Il faut caresser la scene," he says, kissing the black-draped desk. Then, moving into English: "Welcome and thank you for coming. This is an actor's view of his profession. Of the art of acting."

Never mind Pope. To my generation Sydow was God. He was celestial from the minute he played chess with Death in The Seventh Seal, his first role for Bergman. "I was young and he asked me to play the knight. I said, 'But the knight has no lines!' In Bergman's original play he has had his tongue cut out, he just goes, 'Ugh, ugh.' But Bergman assured me, 'No, no, in the film he speaks!'" He did and Sydow's star was born.

"My gratitude to Bergman has no limits," says Sydow. "He was the best director I ever worked with." He wasn't a demonstrative genius, Sydow says. He hardly even talked over the actors' roles with them. "The first rehearsal would be a blocking session. But the blocking immediately gave you the character's psychological rhythm, and his depths."

In Hollywood, where Sydow was lured by the chance to play Jesus in The Greatest Story Ever Told, he had to forge his own techniques for finding a role's depths. Though the Biblical epic fizzled—"the director said he would emphasize Jesus's human side but it didn't turn out that way"—it left Sydow with a sudden up-for-grabs star status.

"Hollywood didn't know what to do with me. I was foreign, so I was offered villains or sinister professors, or priests and martyrs."

Or, between the two extremes, sinister priests. The Exorcist made Sydow world-famous as the demon-evicting cleric who comes to a sticky end. Baddie roles multiplied, including kitten-stroking Blofeld in the Bond movie Never Say Never Again. This opens a disquisition on the nightmares of the multiple take. "The kitten was not co-operative," says Sydow darkly. "Shot after shot was required. In take 26 the cat was brilliant. But I had lost all my spontaneity." The man of doom has told a funny story—almost. After that there are several sombre drolleries. Does an actor take his role home with him? "Journalists always ask me that. They say, is your wife bothered to live with a contract killer, a priest fighting Satan, or Jesus?" Answer: no, although as soon as he accepts a role Sydow does discipline himself to think of it as "I" not "him." "I want to know all about his life before the story starts. I want to know his dreams."

When the class is opened up to the floor, hands shoot up. Sydow cannot tell at first where each one is—"Excuse me, I am blinded by these lights"—and the high-priest of thespians seems momentarily more like a beast at bay. Especially when one of the evening's last questioners wounds him, no doubt innocently, with a query that goes straight to the actor's heart. Why did Sydow not take an offered important role, written specially for him, in Bergman's swansong masterpiece Fanny and Alexander? Had he by then (the question almost implies) sold out to Hollywood?

Sydow dances on a pin, trying to explain. He wanted to do it, he says. But his American agent asked too high a price. Sydow kept telling him, "You must make this happen." But the role finally went to someone else. "I was very upset at the time," he concludes with a mournful growl. "Very upset."

There is a pause. The eyes blink above the sparkling moons of his reading specs. Suddenly—and movingly—Sydow doesn't seem to be telling us about drama. He seems to be a drama himself.