Jean-Louis Trintignant has been, for better than half a century, one of the great stealth actors of the movies. He knows how to catch an audience unaware.

In his latest film, Michael Haneke’s “Amour,” the first surprise, in a way, is simply his presence. His last major role was in Patrice Chereau’s florid pansexual soap opera “Those Who Love Me Can Take the Train,” 14 years ago – and most filmgoers assumed he had retired.

The second, even better, surprise is the quiet confidence of his performance. He seems frailer than we remember him, of course; his face is lined and a little puffy, and his hair, once impeccable, now has that every-which-way look that old guys get. At the outset of the film (opening Friday in Charlotte) you might be a bit worried for him, because the part (written for him by Haneke) is so demanding.

Playing a man caring for his dying wife (Emmanuelle Riva), Trintignant appears in practically every scene, and the movie is, besides, almost literally a chamber piece. After the first few minutes, the action takes place entirely within the walls of the couple’s Paris apartment. But he takes his backbreaking job in stride, and although his gait, in beat-up trainers, is more deliberate than it was, emotionally he’s as sure-footed as ever. Trintignant never was a large man, and age has made him smaller, but he remains, at 82, an actor who can put a movie on his shoulders and carry it.

“The best actors in the world,” he once said, “are those who feel the most and show the least.” This aesthetic of feeling the most and showing the least can be tricky – there’s a fine line between underacting and nonacting – and it isn’t always rewarded at prize-giving time, when flashier turns tend to carry the day.

When Trintignant was named best actor (for “Amour”) at the European Film Awards, it was his first acting honor in four decades. He was not, in fact, heavily laureled even in the period of his greatest success, the 1960s and ’70s, when he starred in more than his share of international hits – “A Man and a Woman” (1966), directed by Claude Lelouch; Eric Rohmer’s “My Night at Maud’s” (1969); Costa-Gavras’ “Z” (1969); and Bernardo Bertolucci’s “Conformist” (1970) – and seemed to be working constantly, primarily in his native France, sometimes elsewhere in the world.

He was always a hard actor to get a fix on, though, because he never really had a type, and he didn’t take especially flamboyant, awards-ready roles, either. What he had – and what kept him in demand – was an extraordinary gift for playing ordinary men.

He had that right from the start of his career, as you could see in his first feature film, Roger Vadim’s “And God Created Woman” (1956), in which the camera seems to take no notice of him for the longest time – it is otherwise engaged, training a close eye on the startling, young Brigitte Bardot – until, little by little, he becomes the most interesting character in the picture. He keeps his thoughts and feelings to himself until he needs them. Toward the end, when he springs his emotional surprises, their effect is powerful.

This sort of slow-building performance, patient and crafty, became, over time, his characteristic style, and directors began to understand that he was an unusual, even a unique, kind of movie star: He didn’t need big scenes to make his points. He didn’t, for that matter, even require all that much screen time.

Remarkably average

Trintignant appears to have realized early on that he was, in the usual terms of movie stardom, only an average specimen of homo cinematicus: of modest height, medium good looking, possessed of a pleasant, expressive, but not terribly memorable voice.

He wasn’t distinctive enough to settle into a particular character type, either: not a working-class hero like Jean Gabin, or an aristocrat like Pierre Fresnay, or a wise guy like Jean-Paul Belmondo, or an existentialist heartthrob like his “Z” co-star Yves Montand. What he chose to do was amazing. He emphasized his averageness, turned his lack of apparent definition into a weird kind of strength. In movie after movie he presents himself as a man so unremarkable that you have to wonder if anything at all is going on underneath that opaque surface. And then slowly, painstakingly, he unwraps the package and shows you what’s inside. He always seems cautious and watchful, waiting for the moment when he can (or must) reveal himself.

In an unusual number of his films his character is shown framed in a window, ever on the inside looking out. Something about Trintignant – a stubborn, willful mysteriousness – seems to make directors see him that way.

In “My Night at Maud’s,” in which Trintignant plays a provincial engineer trying to resolve the philosophical contradictions of his feelings and his principles, Rohmer allows his actor to revel in the character’s indeterminacy – to explore every nuance of a puzzled, irresolute life – and Trintignant looks perfectly at home in that role. He’s able to be lucid about men who are mysteries to themselves, a talent that Bertolucci makes gaudier (and more poetic) use of in “The Conformist,” whose title character yearns for a sort of social normality he doesn’t quite feel.

The tense fascist played by Trintignant in that movie is so tightly buttoned up that he appears on the verge of exploding in a million tiny fragments at any given moment. In this role he restricts his gestures even more rigorously than usual. His stride is short and quick, his hands stay in his pockets; even his hat looks a half size too small. He moves through the world like a bullet seeking a target.

Limitations as assets

He has always been an actor who makes virtues of his limitations, and though those limitations are more pronounced than ever, he’s still doing it.

The many and sudden irritabilities of old age are done full justice in this latest performance, the irksome hesitations of slowed thought and reduced mobility, the unshakable fatigue, the explosive impatience. This performance feels like a kind of apotheosis, the culmination of this actor’s craft or sullen art.

The story of “Amour” is constructed to prepare us, moment by painful moment, for an unexpected end. Trintignant delivers the surprise as he always has and, as always, makes it seem inevitable.