According to legend, it was the painter Hippolyte Délaroche who, on seeing the first daguerrotypes exhibited in Paris in 1839, let out the notorious cry of despair La peinture est morte! That painting was dead or dying soon became a critical cliche, one repeated throughout the 20th century. It is an idea that has haunted Gerhard Richter during a 50-year painting career that "officially began", as he tells it, with a photograph. It has haunted him precisely because of how well he paints.
Moving between styles and media, Richter has been hailed as "the Pablo Picasso of the 21st century", "an artist beyond isms", "an enigma" - often with reference to Délaroche's oracle. Some critics take the variety in his work to signal a conviction that painting is obsolete; others protest that he is a "true believer", who paints to prove that painting lives. Richter himself has said all sorts of things. "Pictures which are interpretable and which have a meaning," he insists, "are bad pictures." Paul Moorhouse, the curator of the show at the National Portrait Gallery, has made the wager that Richter's work, in all its modes - from exquisitely realistic renderings to pure abstractions such as the 4900 Colours shown at the Serpentine last autumn - possesses a nebulous coherence. "People look at the variety and are bewildered," Moorhouse told me. "If you want to understand what it's all about ... look at the portraits."
Richter has resisted attempts to use biography to prise "meaning" from his work. Yet it is clear his experiences growing up under two totalitarian regimes helped shape the commitment to "continual uncertainty" that characterises his aesthetics. Richter was born in 1932 in Dresden. In 1935, his family moved to Reichenau, in what is now Poland, so that his father could take up a post as a schoolteacher; in 1942, they relocated to the still more provincial village of Waltersdorf. While his father, like most government functionaries, joined the Nazi party and fought on the eastern front, the young artist remained a step removed. "Hitler, soldiers, all that was for plebeians," he recalls, "whereas my mother always kept me close to 'culture'." Paintings of Mustang bombers and Phantom Interceptors that Richter produced in the mid-60s, together with his aerial views of European cities in oils and lithographs, evoke the nights of February 1945, when Dresden (100km from Waltersdorf) burned under 4,000 tonnes of US explosives. In 1946, his father straggled home from a Russian prisoner-of-war camp, and was barred from teaching under the new de-Nazification laws. "He shared most fathers' fate at the time," the artist says, "nobody wanted them."
Several paintings in the current exhibition reflect Richter's sense of belonging, literally and spiritually, to a "fatherless" generation. 48 Portraits is a pantheon of black and white headshots depicting male, mostly European, leaders in cultural and scientific fields - Alban Berg, Franz Kafka, Albert Einstein. Traumatised by his father's decline and by the disgrace of Nazi leadership, Richter gestures towards an alternative set of ancestors, representing them as they appeared in popular encyclopedias, rather than after the heraldic fashion of fascist art.
Horst with Dog (1964), also in the show, is a photo portrait in black and white in which Richter's father, identified only by his first name, appears obscured by horizontal streaks like lines of TV static. Richter renders Horst at once hideous and pitiable, a Dr Caligari double whose rumpled clothes suggest he is down on his luck. The pet simpering on his knee makes him all the more grotesque.
The final room in the exhibition contains more recent, colour paintings of Moritz, Richter's son by his third wife, Sabine. In three varyingly abstracted versions of a single photograph - among the most intimate of Richter's numerous autobiographical images - the infant's wide eyes reflect the apprehension, as well as tenderness, of the parent beholding him.
The "father problem" that the young Richter shared with many Germans of his generation anticipated his ambivalent attitude towards the people and institutions he encountered as a young artist. From the age of 16, he was determined to become a painter: his first art-related job involved producing communist banners. He also worked as a painter of signs and stage sets, before being accepted into the Dresden art academy in 1950. For five years, Richter studied amid the berubbled moonscape of Dresden, mastering the heroic style promulgated by the new regime and specialising in murals. He has never fully abandoned the desire to paint "the things one sees and which exist" that was instilled in him during these years. But his willingness to accede to the dogmas of socialist realism crumbled as he discovered the alternative styles thriving across the border.
In 1959, he travelled to Kassell in West Germany to attend the second Documenta exhibition, which presented a wide range of modernist work. Looking at the abstract expressionist paintings there transformed him. Jackson Pollock and Lucio Fontana, he later joked, were his "real reason for leaving the GDR". In 1960, he fled with his first wife, Ema, to Düsseldorf and enrolled in the city's art academy, where Joseph Beuys had just begun to teach. Reproductions in the Dresden library stopped at impressionism. Düsseldorf, by contrast, invited Richter to explore abstract expressionism, dada collage and decollage, pop and radical varieties of "anti-art".
For a time, he flourished. Eventually, however, the modernist freedoms driving him to "paint through the whole history of painting" brought him to an impasse. He found he could not fully commit to gestural abstraction, which to him seemed to rely too much on the artist's subjectivity. Nor could he embrace the anti-art ideals of Beuys and the Fluxus group, which were deeply hostile to his form of studio practice. This time his "fundamental aversion to all beliefs and ideologies" turned Richter against the capitalist west. He was particularly put off by the cults of personality surrounding his contemporaries. It was Künstlerscheisse, he later complained - "artist-bullshit".
By 1962 Richter "had had enough of bloody painting", when chance dropped a new "pretext" into his lap: a photo of French actress Brigitte Bardot. He incorporated it into the abstract canvas he was working on (now lost) and burned all his old work. Around the same time, he began collecting the photographs that comprise Atlas, the ever-expanding compendium of source images from whose panels he still draws, ranging from personal snapshots to celebrity glam-shots, from advertisements to pornography, landscape postcards to photographs of concentration camps - which he has never used, because he found them "unpaintable".
Richter later remarked: "Photographs were the way forward. I'm shocked now that the story seems clear, because it didn't seem clear at the time." What kind of solution did photos offer? Critics often quote Richter in his Notes 1964-65: "I like everything that has no style." But they almost always omit the line in brackets that follows: "(Because style is violence, and I am not violent.)" His rejection of totalising political or artistic ideologies, and his suspicion of paternal authority, mirror his refusal to settle down to any one way of painting. Through his photo portraits he developed a "styleless" style - that is, a way to continue painting without capitulating to authority or asserting it himself.
The portraits at the National Portrait Gallery lack style in the sense that each has been copied from an automatic, mechanically reproducible medium. Richter has described and demystified his method: he projects copies of photos on to canvas, traces them in pencil, then fills them out in paint. Yet, if the automatic quality of this process helps him evoke an "anti-sensibility", it hardly grants his canvases the special access to the world that early champions of photography took to be the defining trait of the medium. In an interview in the mid-60s, he asserted: "A portrait can never come closer to the sitter than when it is a very good likeness. For this reason, among others, it is far better to paint a portrait from a photograph." Richter favours photography not because it guarantees a connection between the surface appearance of the artwork and some reality behind it, but because it renounces any such claim.
The results are diverse. He has painted both black and white and colour portraits - of celebrities, such as Jackie Kennedy or Queen Elizabeth; anonymous individuals; and some family members, close friends and professional associates. There are two self-portraits from 1996 in which Richter, bled into a semi-transparent blear, looks down in the attitude of Dürer's Melancolia. His clarity of vision also varies. Although he has resisted allowing the gesture to become an "identity tag", he usually defaces his photo paintings. Sometimes, he produces a "blur", as if the camera that took the snapshot had been out of focus, by feathering the still wet paint with a dry brush. In other cases, he scrapes into the drying portrait with a ruler or spatula.
Writing for the catalogue of the 2002 Museum of Modern Art retrospective that cemented Richter's reputation, the curator Robert Storr described the artist's impulses in semi-religious terms: "doubt" and "belief". Particularly when set beside the Vermeer-like perfection of the few that Richter spares, the "blurred" and gashed canvases evoke the strength of conviction that it must take to mar them. These are the devotional gestures of a profound agnostic. The agnosticism, realised in the photoportraits, also applies to Richter's abstractions, or to the panes of glass and tinted mirrors for which he is famous. In each of his styles, Richter compels us to consider the act of looking - he balances longing for something behind what is represented with an insistence that we can never know what is there.
Moorhouse has taken pains to draw attention to the philosophical dimensions of Richter's style. "Illusion - or rather appearance, semblance - is the theme of my life," he quotes him as saying: "All that is, seems, and is visible to us because we perceive it by the reflected light of semblance." Richter's language echoes doubts about human knowledge that are as old as Plato's allegory of the cave. It also has more recent, specifically German, antecedents. Kant set out the axiom that we can never know "things in themselves", but only how they appear in experience. Schopenhauer reprised Kant's theory, speaking of the world as mere "representation". Nietzsche, in whose work Richter immersed himself as a teenager, drove the process to its conclusion, doing away with essence all together. "What could I say about any essence," Nietzsche asks, "except to name the attributes of its appearance?" Richter's terminology is more slippery than that codified by philosophers, yet his essays and interviews make it clear that he shares their concerns.
The sense that reality is unknowable (and, so, unrepresentable) reinforces the special relationship that Richter's paintings have with death. "When you take a photograph you get an immediate fracture," Moorhouse says. "When you take a painting, you open the gap even further. When you are painting from photographs that are taken years ago, the appearance becomes a ghost." Photographs, particularly black and white, have often been viewed this way. At an exhibition of daguerreotypes even earlier than the one attended by Délaroche, viewers are said to have turned away from the wraith-like portrait plates in terror. Never having seen an image of a person separated from its "original", they were spooked. By the 1860s, when "spirit photographers" in the US and Europe were reaping small fortunes, using multiple exposure and other tricks to produce images of the beyond, it had become obvious that the new medium had come into its own as just that: a medium. Photography is not only a means of representation but also, as the late German novelist WG Sebald put it, "a way of making ghosts".
Richter himself worked as a photographer's assistant developing photos when he was young (or so he has said). And he has emphasised the impact of this apprenticeship. "The masses of photographs that passed through the developing bath every day," he has said, "may well have caused a lasting trauma." His photoportraits make us conscious not only of the loss of reality in images, but also of the reality of loss that Richter, as a child of Germany's zero hour, had to confront. They constitute a form of remembrance of what they know they cannot fully represent.
• Gerhard Richter Portraits is at the National Portrait Gallery, London WC2 (0844 579 1924), until 31 May.
