Big predictions can take time to come true. When David Hockney, a working-class Yorkshire lad, left his Bradford school at 16 to go to art school, his English teacher and form master assessed him in these terms: "He has undoubted ability in art, especially in cartoon and sign-writing work. Although fundamentally a serious-minded boy, he has allowed his form-mates from his third-form days, to make him an almost legendary figure of fun. It is only in his last year that he has shown his serious side—but we have enjoyed his company." The headmaster appended a kindly valediction: "Best wishes to him in his new start. He will be glad to be rid of the 'figure of fun' & to establish himself as a sincere & serious person by steady work & merit."

For half a century, the boy from Bradford, as he still often calls himself, has been hard at it. He's 69 now, and the honors have accumulated. New work shows up constantly in commercial galleries as well as in such institutional extravaganzas as the Whitney Biennial of 2004, in New York City, and the Royal Academy of Arts Summer Exhibition that same year, in London.

"Hockney is so famous, so popular, such a great talker and character that it's easy to take him for granted as an artist," Jonathan Jones, the art critic of The Guardian, observed not long ago. "If you’re a critic, it's tempting to give him a bash. But Hockney is a significant modern painter. He is one of only a handful of 20th-century British artists who added anything to the image bank of the world’s imagination."

A major retrospective is an occasion, and such a thing is before us now. "David Hockney Portraits"—featuring some 150 paintings, drawings, etchings, photographic collages and watercolors—covers the work of more than 50 years. Alphabetically, the list of sitters in the show's catalog runs from the poet W. H. Auden (whom Hockney remembers as grumpy) to Karen Wright, editor of Modern Painters magazine, mostly by way of people only their immediate circles will have heard of. The show made its debut at the Museum of Fine Arts, Boston, in February and is now on view at the Los Angeles County Museum of Art through September 4. Los Angeles is one of the cities to which Hockney's ties are closest; the other is London, where the tour concludes at the National Portrait Gallery (October 12, 2006 to January 21, 2007).

"There are no glamorous people in this show," Hockney said in Boston. The history of Western art has produced two basic types of portraitist. On the one hand, the professional brush for hire, who specializes in the rich and mighty: Hans Holbein the Younger, say, or Frans Hals, Sir Anthony Van Dyck or John Singer Sargent. Then there are the inveterate students of human nature: Albrecht Dürer, Michelangelo, Rembrandt van Rijn, Vincent van Gogh. Hockney places himself squarely in the latter camp: a portraitist for art’s sake. The commissions he has accepted over the decades are scarcely enough to count on the fingers of one hand.

Starting in spring 2005, Hockney has been immersed in a project of a very different sort: the landscapes of his native Yorkshire through the four seasons. "Portraits of trees!" he quips. Though he made suggestions for the current show, he didn't choose the pictures. "Ordinarily a show of portraits by one artist can be boring," he says. "The paintings must be interesting as paintings. That's why I wouldn't have thought of this. I've never thought of myself as a portraitist. But then I thought: I did portraits all the time." To encounter the paintings in full-court press is an occasion as novel for him as it is for any visitor.

He is not displeased, nor need the visitor be, that the definition of a portrait has sometimes been stretched beyond the breaking point. Does the vaguely autobiographical series "A Rake's Progress" (1961-63)—in 16 satirical etchings of his first impressions of America, inspired by the 18th-century printmaker William Hogarth—in any sense constitute a portrait? Not really, any more than does a full-length rear view of a nude in a swimming pool. Even so, there are aspects of Hockney's work—the landscapes (Grand Canyon, the Hollywood Hills), exotic locations (formal gardens of Japan, the Alhambra), the theater (ravishing sets for opera productions of Mozart, Wagner, Stravinsky, Ravel)—even the most latitudinarian curators would have had to exclude. No matter. "Art's subject is the human clay," W. H. Auden wrote in his long "Letter to Lord Byron." Hockney loves the passage and quotes it often: "To me Art's subject is the human clay, / And landscape but a background to a torso; / All Cézanne's apples I would give away / For one small Goya or a Daumier." Portraits—people—prove a uniquely apt lens for bringing Hockney's life's work into focus. It might, in fact, have been a neat touch to recycle Hockney's title for his first solo show, in 1963: "Pictures with People In."

The Boston opening was a glittering affair, sumptuously catered, with free-flowing champagne and an open bar. Friends, portrait sitters and collectors had flown in from across two oceans. Seeing the portraits in the same galleries as many of the living originals was illuminating. "Art makes me see!" Hockney says, recalling the time in Chicago in 1995 when the great Monet retrospective opened his eyes to the bushes on Michigan Avenue, to the "beauty of a shadow on a leaf.” In Boston, that remark took on new resonance. Stepping from the exhibition over to the smoking tent (the artist is a militant smoker), one had further opportunity to study quite a few of his subjects. The spontaneous play of expression—of glance returned and glance deflected, of curled lip or rising eyebrow—cried out for a great sketch artist's quick, accurate hand. Alas, the man of the hour wasn't working that night.

Called to the microphone in an auditorium filled to capacity, Hockney was brief in the extreme. "I've had one or two other big exhibitions," he began, beaming shyly (or was that a blush?). "It would never have occurred to me to do portraits. I don't know what to say. Thank you all." His tweedy clothes and his build, stooped from a lifetime behind the easel, recalled a bluff, outdoorsy country squire. Dancing eyes and an impish smile belied his years. His speech could not have lasted 60 seconds, yet his glow of deep pleasure gave it an eloquence.

On the whole, Hockney liked what he saw. Strolling through the exhibition the next morning for another private look, he gave an approving nod to the first of his rare commissioned portraits: the ailing Sir David Webster, retiring general administrator of the Royal Opera House, Covent Garden, painted in 1971. Against a blank wall, Sir David is seen in profile, gazing like a weary eagle from the roost of a Marcel Breuer chair. A vase of coral-pink tulips—Hockney's favorite flower—placed low on a glass coffee table brings the composition into coolly formal balance.

The artist looked more dubious about The Photographer and his Daughter, from 2005, depicting Jim McHugh, a noted Los Angeles professional, and his teenage daughter, Chloe. Provocative hand on hip, Chloe glares out from the canvas as her father looks on from a chair, rubbing his chin. (Some viewers have been reminded of the unsettling eroticism of Balthus, the French-Polish antimodernist.) The night before, pretty in pink, Chloe had accommodated the news crews by standing by the painting and striking the same pose. But the canvas as a whole is a study in powdery blues, which Hockney is now thinking might look too dry. His preferred ratio of oil to pigment would explain that. "I don't use much oil," he notes. "I left Los Angeles just after finishing this one. I would have varnished it otherwise. That makes the darks richer too." He licks a finger and runs it over one of Chloe's blue eyes, scandalizing a curator. "See the difference?" Yes, for a second or two. Then the trace evaporates.

Over the decades, Hockney has evolved into the living artist most deserving of the title Old Master: eager pupil to Giotto, Jan van Eyck, Leonardo, Caravaggio, Velázquez, Rembrandt, Vermeer and Ingres. His principal forebears among the moderns include van Gogh and, above all, Picasso, whose 30-plus volume catalogue raisonné ranks as a prize possession. To Hockney's regret, he and Picasso never met. But after the Spaniard's death in 1973, Hockney came to know and work with Aldo Crommelynck, Picasso's printer for a quarter century, and Crommelynck told Hockney that he was sure "Pablo" would have liked him. Hockney paid posthumous tribute to Picasso in 1973-74 with his etching Artist and Model—showing himself (nude) and the older painter (in signature sailor's garb) seated face to face across a table.

The Hockney depicted in Artist and Model looks seriously studious, but the image is graceful and witty too. Did the figure of fun from the Bradford Grammar School ever go away? Peter Schlesinger, the young California Adonis who wandered into Hockney's drawing class at UCLA in 1966 and became his muse and lover for the next five years, once described his first glimpse of the artist this way: "He was a bleached blond; wearing a tomato-red suit, a green-and-white polka-dot tie with a matching hat, and round black cartoon glasses."

Revisiting the artist's life via the portraits in the exhibition may make viewers wish to turn back the clock to see him as he was then; thanks to the movies, they can. The bleached blond—Rodinesque of stature, petulant, languid, his nose to the canvas—is on view in all his outlandish glory in the strange, once scandalous, art-house film A Bigger Splash by the director and screenwriter Jack Hazan, first released in 1975. In a seamless blend of documentary and speculative fiction—part Proust, part Warhol—the film traces the slow death of Hockney's romance with Schlesinger. When the film was made, Hockney was but a boy wonder on the art scene, nothing near the full-blown media star he was to become. But he made good copy. As a figurative painter coming up in an age of abstraction, he had the appeal of the eccentric. In a Carol Channing/village-idiot hairdo, wearing mismatched socks, cutting a moody swath through what Time had dubbed Swinging London, he seemed rather a clown, if mostly a sad one.

Yet within the flow of Hazan's narrative, the viewer can already catch sight of Hockneys that by now stand as icons of 20th-century art: those vistas of California's cloudless skies, palm trees (stout or spindly) and, oh, those swimming pools. More to our immediate point, we catch glimpses of standout paintings from the current show: Beverly Hills Housewife (1966), for instance, which depicts Betty Freeman, who might be more accurately identified as a photographer and patron of new music. Likewise present: Henry Geldzahler and Christopher Scott, from 1969. An early and powerful champion of Hockney's, Geldzahler held a succession of influential cultural positions in New York (including curator of 20th-century art at the Metropolitan Museum of Art) until his death in 1994. He was not handsome, but he had a presence. In the double portrait, he imperializes the center of a pink Art Deco sofa vaguely reminiscent of an open seashell. His portly frame is clothed in a three-piece business suit and tie, minus the jacket. Skin shows above the sock on his right shin. Lips parted, sedentary, judgmental and remote, he stares straight out from behind rimless glasses, freezing out his partner, Scott, who stands in profile at far right in a belted trench coat. In Hazan's film, Geldzahler is seen studying his glasses as Hockney has painted them, an exercise visitors to the current show will find well worth their while. The highlights on the lenses and reflections of details in the room evoke the uncanny clarity of early Flemish painters.

The formality and stillness of the scene have put some critics in mind of a latter-day Renaissance Annunciation. Old Master allusions like this crop up all over the place in discussions of Hockney's art. To Barbara Shapiro, co-curator of the current show (with Sarah Howgate, of the National Portrait Gallery, London), this makes perfect sense. "Thanks to his book Secret Knowledge, people know that David is interested in the optical techniques of the Old Masters," she says. "But what they don’t necessarily get is how much he loves the paintings as pictures, for the spaces they create and the stories they tell and the way they bring to life people from long ago and far away. More than other contemporary artists, he goes to exhibitions of artists from the past for the sheer excitement of it. Every time I visit his house, he's showing me art books and catalogs. His collection is amazing. It's exciting to talk with him about what he's looking at."

Hockney's immersion in the art of the past can be evident even in his depiction of a single face. In 1989, he would paint Geldzahler again—by now snowy-bearded—in a knit cap and plaid hunting jacket looking for all the world like a Titian doge. Or take the double portrait Mr. and Mrs. Clark and Percy, depicting friends of the artist's from the London fashion scene and their cat. Mrs. Clark—nee Celia Birtwell—soft and guileless in a floor-length robe of deep purple velvet, poses to one side of a half-shuttered French window. Mr. Ossie Clark, barefoot, in a sweater, a cigarette in hand, reclines in a cane-back metal chair, his air tense and guarded. On Mr. Clark's lap, a snow-white cat gives the viewer its back. The portrait has been likened—fancifully—to the Van Eyck masterpiece The Arnolfini Wedding, a painting that Hockney examined in his book Secret Knowledge.

Still: that Old Master mantle. Does it compute to confer such gravitas on an artist so easy to enjoy? The keynotes of his work throughout a long career have been curiosity and joie de vivre, combined with a certain propensity to wear his heart on his sleeve. Like Matisse, he is a symphonist of the feel-good palette. His frank appreciation of male skin, especially in pools and showers, has opened him up to imputations of decadence and frivolity. "It's useful to recall," wrote Time, "that one of Hockney's enduring contributions to the history of the nude—we mean this—is the tan line." Besides, there is the matter of his technical experimentation. We're talking Polaroids here, video stills, photocopies, art by fax and, in a bold leap backward, the cumbersome camera lucida.

At the time, these departures could seem aberrant, misguided or simply silly. "David Hockney Portraits" offers a panorama of the work in virtually any medium you like, and the verdict, in retrospect, looks very different. As a wall label for the Boston installation proclaimed, "Hockney is unafraid of change." True enough, where technique is concerned. But changes in technique have served a consistent purpose: to approach, ever more closely, the circle of intimates who are the objects of his constant gaze.

Of course, one's vantage point affects the view. Deeply. Perspective, as Hockney once explained to a new acquaintance at a dinner party, is a matter of life and death. One-point perspective as codified in the Renaissance, he demonstrated with a little illustration, is a dead view, a mechanical view, the view of an unmoving, unblinking eye. The eye, in short, of the camera. But the human eye doesn't see like that. It's constantly in motion, even when we are standing still. Rather than one vanishing point, there should be vanishing points without number. "We’re 3-D creatures," Hockney says. The artist's task, as he conceives it, is to capture the act of seeing as we experience it in the confines of two dimensions.

Hence, for instance, the experimental collages of Polaroids, snapshots and video stills that Hockney began making in the early 1980s and took to calling "joiners." The process taught him a lot about creating a sense of movement and feeling of space, and about collapsing an extended span of time into a single image. It has been said that with this technique of overlapping photographic images, and their inevitable slight discontinuities in time, Hockney taught the camera to draw. Thus he has taken what he understands to have been Picasso's Cubist agenda further. The point is not so much to show all sides of an object at the same time, but rather to enter into much closer proximity to it, to explore it more intimately. Doing so takes time, which may be why Hockney so seldom shows figures frozen in dramatic action. Hold a gesture and you get a pose: something inert, dead, fit only for the camera. The stillness in a Hockney painting is in a sense the summation of movement not seen: movements of the body, movements of thought, encompassing, as a snapshot cannot, stretches of time, rather than a single point.

That quality is one he looks for in the work of other artists too. Hockney himself has sat for portraits by many artists, from Warhol to British artist Lucian Freud. For the exacting Freud, he posed without regrets for a marathon 120 hours. "You see the layers," he says. Indeed, the weary-eyed portrait reveals hurts and gloom he does not always care to show in company. Not that Hockney doesn't see them himself. They are there in unsparing self-portraits from the past two decades. What's different about the self-portraits, though, is the fierce quality of Hockney's gaze locked on the mirror's.

In whatever medium, what drives Hockney is the need to render the act of looking. The faces he has chosen to look at are those of friends, lovers and other members of his household, including pets. "Oh, you're painting your dog," a friend once exclaimed in surprise as she walked into Hockney's studio to find a painting of his dachshund Stanley on the easel.

"No," came the reply. "I'm painting my love for my dog."

And kin: Hockney’s father, Kenneth, an accountant's clerk of independent political convictions and fastidious sartorial habits; his mother, Laura, a Methodist and strict vegetarian, pensive and petite; his sister, Margaret; his brother Paul. Studying the parents' faces, it strikes me that David has inherited Kenneth's face and Laura's eyes. But family resemblances are elusive; a few steps on, I change my mind. "If you don't know the person," Hockney has said, "you really don't know if you've got a likeness at all."

Kenneth, as it happens, was the subject of the first painting Hockney ever sold: Portrait of My Father (1955), which was also one of his first oils. Recognizably a Hockney, yet tense and hardly prophetic in its morose tonality of blacks and browns, it was originally shown in the mid-1950s at the biennial Yorkshire Artists Exhibition in Leeds, principally a vehicle for local art teachers. Hockney put no price on it. He figured no one would buy it anyway. Even so, the opening on a Saturday afternoon, with free tea and sandwiches, struck him as "a great event, an enormous event." (He was in his late teens.) Imagine his amazement when a stranger offered him ten pounds. Since his father had bought the raw canvas ("I'd just done the marks on it"), Hockney wanted to clear the sale with him first. Kenneth said to take the money ("You can do another").

But there's more to the story. Not only had Hockney père bought the canvas, he had also set up the easel, a chair for himself to sit in and mirrors in which to watch his son's progress. He kibitzed constantly, complaining notably about the muddy colors. Hockney talked back: "Oh, no, you're wrong, this is how you have to do it, this is how they paint in the art school."

That spirited debate set a pattern Hockney still follows when the occasion warrants. Even now, he will set up mirrors for his sitters from time to time. Charlie Sitting, painted in 2005, is a result of this process. Poetic and allusive, the work seems a sort of reverse-gender illustration of the Victorian ballad "After the Ball." Dressed in a tuxedo, the subject—Charlie Scheips, a freelance curator and former Hockney assistant—slouches in a chair, tie undone, a flute of champagne in hand, a faraway look in his averted eyes.

Actually, Scheips told me at the Boston opening, the suggestion of heartbreak is pure illusion. Scheips donned his after-six finery early one morning at Hockney's request, then assumed the position. Knowing his model's interest in seeing him work, Hockney set up the mirror on which Scheips' eyes are fixed. Another painting from the same year, Self-portrait with Charlie, depicts Scheips in his dual role as model and onlooker, perched on a side table, frankly absorbed in Hockney's unseen canvas-within-the-canvas.

Hockney doesn't mind being watched. On the contrary, it's what he lives for: "'I'm just looking,' people say. 'Just looking!' Looking is hard. Most people don't."

Matthew Gurewitsch writes on art and culture for such publications as the New York Times and the Wall Street Journal.