In 2008, a decade after his father's death and a few months shy of his 40th birthday, the Norwegian novelist Karl Ove Knausgaard started to write the truth about his life.
At the time, he was living in an apartment in Malmö, Sweden, with his second wife, the author Linda Boström, and their three young children, Vanja, Heidi and John. With his 1998 debut about a teacher who falls for his teenage pupil, Out of the World, Knausgaard had become the only first-time novelist ever to win the Norwegian Critics' Prize; its angel-themed follow-up, A Time for Everything (2004) had brought further plaudits. He was, in short, a success.
Yet when we meet, at the Tate in London on a late summer's day, he recalls 2008 as being a moment of imminent crisis in which "everything was grey somehow. And I remember thinking: how is it possible to have three beautiful children, to be doing the one thing I had always wanted to do, getting my books published, and yet still not be appreciating life? That was the starting point for My Struggle."
Published in Norway in six breathless instalments between 2009 and 2011, and subsequently translated into English at a rate of roughly one volume a year, the 3,600 autobiographical pages of My Struggle represent one of the most singular and divisive literary achievements of our time.
Knausgaard's prose is unapologetically plain, written in haste and without much appetite for revision (he dispatched the 600-page fifth book in eight weeks). His focus dwells as often on the banal as the sublime. Among the objects of his scrutiny in the final volume, newly translated into English as The End, are the changing colours of prawns when cooked ("alive they looked almost like office workers of the ocean, in death like a company of ballet dancers"), and Adolf Hitler, to whom the author devotes an entire 400-page essay, midway through the narrative.
Yet the overall picture Knausgaard creates of his life to date – from a childhood in rural Norway lived in fear of his violent father, through his clumsy adolescent flirtations with writing and women, to his humdrum daily routine raising children of his own – combines photorealistic clarity and philosophical insight to utterly absorbing effect. Read the whole saga and, by the end, you may feel you know its author more intimately than you know many of your friends, perhaps better even than you know yourself.
For Knausgaard, My Struggle is "basically a book about a son wanting or trying to become a father" and was always intended less as an act of self-portraiture than as a stab at self-discovery. "I have never been interested in presenting myself," he tells me, in fluent, accented English, over coffee in the Tate's tea room. "The book is something completely different: it is the search for meaning." He says he laid out his life on the page, "drew a picture of an area where you could go in and look around", blurring the line between fact and fiction by employing a degree of detail that memory alone could not retrieve (in My Struggle, even conversations recalled from decades earlier are related ostensibly verbatim) to map the experiences and encounters that had made him the man he was and, in doing so, identify where he might have misplaced his happiness along the way.
It is, of course, impossible to picture a life in full without putting others in the frame, and not everyone featured in My Struggle felt he'd caught their best angle. Shortly before the publication of the first volume – which includes, among other things, an unsparing description of the dismal circumstances in which Knausgaard's alcoholic father's body was found, surrounded by "overturned bottles, tobacco pouches, dry bread rolls and other rubbish... there was excrement on the sofa, smeared and in lumps" – his uncle threatened legal action, disputing the veracity of his account.
The Scandinavian tabloid press leapt on the story and Knausgaard's project acquired an instant notoriety that it would never shed. His personal reckoning had become public property.
"Journalists called everyone I knew, and they called Linda's family. All they wanted was for someone to say, 'It's a terrible project!' or 'It's ruined our life!' so that then they would have their story. And then, you know, your friends have read it and your friends' friends and your mother's friends..." It is estimated that one in 10 Norwegians now owns a copy of My Struggle – "and I am the one who has done all that. It felt uncontrolled and wild somehow, the whole thing."
When Knausgaard was a few hundred pages into writing The End, Linda suffered a severe bout of depression and was taken to hospital; a candid account of her breakdown and recovery forms the final section of the book. "Linda has stars inside her, and when they shine she shines," Knausgaard writes, "but when they don't, the night is pitch black."
Today, he says that, "for me, that was the hardest part to write in the whole series, I think because by then I knew how the book was being read. One of the consequences – not only of that pressure, of course, but partly that – was that Linda ended up in hospital, and so writing about her again seemed like something you really can't do." And yet, he did it anyway: the live, autobiographical nature of the project made the alternative unthinkable. "It would have been the same thing if she'd broken her leg," he says. "I would have written about that, too."
The End, which opens shortly before the first volume is published, is in many ways the author's attempt to come to terms with the impact of My Struggle before he had even finished writing it. He weighs the toll the book might be taking on those closest to him, including his children (now aged 14, 13, 11 and joined by a fourth, Anne, in 2014) whose personalities and peccadilloes he relates throughout with a combination of affection and impatience. "I will never forgive myself for what I have exposed them to," he writes on the book's final page. "But I did it and I will have to live with it."
Looking back now, he is inclined to judge himself less harshly, not least because seven years on, "the notion of what is public and what is private has been dissolved. My children see documentaries, they see Instagram, everyone is very open: it has become less taboo to expose lives." He adds, "That's not an excuse, just an observation. But I think it's less strange to them."
Which isn't to say that he wishes to equate his children sharing something on Snapchat with the exposure that My Struggle inflicts on them; far from it. "I think literature is completely, completely different, almost the opposite," he says. "It's the search for inner life and truth and soul. If [social media] is the stage, then literature is backstage." While social media promotes what he identifies in the book as "Nazi values" by bombarding our young with a fantasy of "beautiful bodies, beautiful faces, healthy bodies, healthy faces, perfect bodies, perfect faces," literature remains "somewhere ugly stuff and boring stuff and not very nice stuff also must have its place".
In The End, Knausgaard takes potshots at everything from supermarket wheelie baskets ("It was one of the saddest sights I knew, all semblance of human dignity evaporated the moment a person went with that of all options") to Scandinavian society as a whole ("never has any human population been so comfortably dulled in hygge as our own").
But few aspects of My Struggle delve as deep into the realm of the ugly as the author's reminiscences of his father, a former schoolteacher who terrified the young Karl Ove, beat his elder brother, Yngve, then drank himself into oblivion. "My father was a king without a country," Knausgaard writes in The End. "That he died a clown, his nose reddened by blood, in his mother's armchair, changes nothing. To me, he will be king until the day I die."
After I read these words back to Knausgaard he remains silent for a few seconds, his gaze fixed on his coffee cup. "When I started writing My Struggle, my father was still an issue, someone I had in me every day, someone I would dream about – he was still a part of me," he says, at length. "He was such a huge figure for me and now he is just one among many and that feels like a relief." It is a change he credits less to the cathartic effect of pinning his father's ghost to the page – after all, he says, his brother "thinks I am too mild on him in the book" – than to the passage of time.
"I am not the same person as when I started out," says the author towards the end of The End. As his 50th birthday approaches, he has changed again: in place of the rock star hair, leather jacket and intense scowl familiar from the book covers, he sports a tweedy blazer, silvery short back and sides and a gentle smile that suggests he has found, if not the meaning of life, then at least a way to enjoy it better. A few years ago, his marriage to Linda came to an end and he now spends alternate weeks in Sweden and London, where he lives with his British fiancée, who works in publishing.
If Knausgaard's life has moved on, then so has his writing. After producing a four-volume non-fiction sequence built around the seasons (culminating in Summer, published in English in June), he has now embarked on a new kind of novel, one in which Karl Ove Knausgaard will not be making an appearance. "In My Struggle it is one voice, expanded in all directions, and this is many, many voices meeting in one physical place," he tells me. "The challenge is of course getting out of my own way of writing and finding other voices. Maybe I will fail, but I don't want to keep on doing what I have been doing. There is nothing left for me in that.
"My Struggle came from a place of questioning and feelings of inauthenticity and frustration, and almost all of that is gone." He drains his coffee cup and rattles it back into its saucer. "The life will continue – but it will no longer be written about."
The End by Karl Ove Knausgaard (tr Martin Aitken and Don Bartlett) is published by Harvill Secker at £25. To order your copy for £20, call 0844 871 1514 or visit the online Telegraph Bookshop