Knut Hamsun (August 4, 1859 – February 19, 1952) was a Norwegian author. He was praised by King Haakon VII of Norway as Norway's soul. In 1920, he was awarded the Nobel Prize in Literature for the epic Growth of the Soil. He insisted that the main object of modern literature should be the intricacies of the human mind, that writers should describe the "whisper of blood, and the pleading of bone marrow". Hamsun's literary debut was the 1890 psychological novel Hunger, which some critics consider to have been an inspiration for Franz Kafka's classic short story A Hunger Artist.

Hamsun's reputation was severely tarnished by his vehement advocacy of Nazi Germany both before World War II and after Germany occupied Norway in April, 1940. He lionized leading Nazis and in 1943, in the middle of the war, he mailed his Nobel medal to Joseph Goebbels. Later, he visited Hitler and in a eulogy for the German leader published on May 7, 1945 — one day before surrender of the German occupation forces in Norway — Hamsun proclaimed, “He was a warrior, a warrior for mankind, and a prophet of the gospel of justice for all nations.” After the war, due to a finding that Hamsun was in mental decline, efforts to prosecute him for treason were dropped. Nearly 60 years after his death, a recent biographer told a reporter, “We can’t help loving him, though we have hated him all these years. That’s our Hamsun trauma. He’s a ghost that won’t stay in the grave.” In 2009, the Queen of Norway presided over the gala launching of a year long program of commemorations of the 150th anniversary of the author's birth. On August 4, 2009 a Knut Hamsun Center (Hamsunsenteret) was opened in Presteid, Hamarøy island.

Knut Hamsun was born as Knud Pedersen in Lom, Gudbrandsdal, Norway. He was the fourth son (of seven children) of Peder Pedersen and Tora Olsdatter and claimed to have been born in a cottage at Garmostrædet in Garmo 8 miles (13.5 km) from Lom towards Otta, Norway. When he was three, the family moved to Hamsund, Hamarøy in Nordland. They were poor and an uncle had invited them to farm his land for him. At age nine, Knut was separated from his family and lived with his uncle Hans Olsen, who needed help with the post office he ran. Olsen used to beat and starve his nephew, and Hamsun would later state that his chronic nervous difficulties were due to the way his uncle treated him. He saw his uncle as "the old colonial power, England", and himself as "young Germany, asking for Lebensraum".

In 1874, he finally escaped to Lom, Norway. In the next five years, he would pick up any job just for the sake of the money. That included being a store clerk, peddler, shoemaker's apprentice, an assistant to a sheriff, and an elementary school teacher. At 17, he became an apprentice to a ropemaker, and at about the same time he started to write. He spent several years in America, traveling and working at various jobs, and published his impressions under the title Fra det moderne Amerikas Aandsliv (1889). Working all those odd jobs paid off, and he published his first book about it: Den Gaadefulde: En Kjærlighedshistorie fra Nordland (The Enigmatic Man: A Love Story from Northern Norway, 1877). In his second novel Bjørger (1878), he would attempt to imitate Bjørnstjerne Bjørnson's writing style of the Icelandic saga narrative. The melodramatic story follows a poet Bjørger and his love for Laura. This book was published under the pseudonym Knud Pedersen Hamsund. This book would later serve as the basis for Victoria: En Kærligheds Historie (1898; translated as Victoria: A Love Story, 1923).

Knut Hamsun died on February 19, 1952, aged 92, in Grimstad, Norway.

Thomas Mann would describe him "as a descendant of Fyodor Dostoyevsky and Friedrich Nietzsche". Arthur Koestler was a fan of his love stories. H.G. Wells praised Markens Grøde (1917), which when translated in 1920 to Growth of the Soil, Hamsun was awarded the Nobel Prize in Literature. Isaac Bashevis Singer was a fan of modern subjectivism, use of flashbacks, his use of fragmentation, and his lyricism.

Hamsun first received wide acclaim with his 1890 novel Hunger (Sult). The semiautobiographical work described a young writer's descent into near madness as a result of hunger and poverty in the Norwegian capital of Kristiania (modern name Oslo). To many, the novel presages the writings of Franz Kafka and other twentieth century novelists with its internal monologue and bizarre logic.

A theme to which Hamsun often returned is that of the perpetual wanderer, an itinerant stranger (often the narrator) who shows up and insinuates himself into the life of small rural communities. This wanderer theme is central to the novels Mysteries, Pan, Under the Autumn Star, The Last Joy, Vagabonds, and others. Hamsun’s prose often contains rapturous depictions of the natural world, with intimate reflections on the Norwegian woodlands and coastline. For this reason, he has been linked with the spiritual movement known as pantheism. Hamsun saw mankind and nature united in a strong, sometimes mystical bond. This connection between the characters and their natural environment is exemplified in the novels Pan, A Wanderer Plays on Muted Strings, and the epic Growth of the Soil, the novel which is credited with securing him the Nobel Prize in literature in 1920.

A fifteen-volume edition of his complete works was published in 1954. In 2009, to mark the 150-year anniversary of his birth, a new 27-volume edition of his complete works was published, including short stories, poetry, plays, and articles not included in the 1954 edition. For this new edition, all of Hamsun's works underwent slight linguistic modifications in order to make them more accessible to contemporary Norwegian readers. Fresh English translations of two of his major works, Growth of the Soil and Pan, were published in 1998.

Along with August Strindberg, Henrik Ibsen, and Sigrid Undset, these writers became internationally known for their works. Hamsun pioneered psychological literature with techniques of stream of consciousness and interior monologue that would be found in material by James Joyce, Marcel Proust, and Virginia Woolf.

In 1898, Hamsun married Bergljot Goepfert (née Bech), who bore him the daughter Victoria, but the marriage ended in 1906. Hamsun then married Marie Andersen (b. 1881) in 1909 and she would be his companion until the end of his life. With Marie Hamsun he had four children, the sons Tore and Arild and the daughters Elinor and Cecilia. Marie wrote about her life with Hamsun in two memoirs. She was a promising actress when she met Hamsun, but ended her career and traveled with him to Hamarøy. They bought a farm, the idea being "to earn their living as farmers, with his writing providing some additional income". However, after a few years, they decided to move south, to Larvik. In 1918, the couple bought Nørholm, an old and somewhat dilapidated manor house between Lillesand and Grimstad. The main residence was restored and redecorated. Here Hamsun could occupy himself with writing undisturbed, although he often travelled to write in other cities and places (preferably in spartan housing).

Hamsun was a prominent advocate of Germany and German culture, as well as a rhetorical opponent of British imperialism and the Soviet Union, and he supported Germany during both the First and the Second World War. His sympathies were heavily influenced by the impact of the Boer War, seen by Hamsun as British oppression of a small people, as well as by his dislike of the English and distaste for the USA. His international popularity waned because of his support of Vidkun Quisling's National Socialist government. His image as a supporter of both Norwegian and German Nazi ideology was further confirmed when following a 1943 meeting with Germany’s minister of propaganda Joseph Goebbels, he sent Goebbels his Nobel Prize medal as a gift and token of his admiration. While in his 80s, and largely deaf, Hamsun met with Adolf Hitler. His audience with him is recorded to have been mostly Hamsun complaining about the Nazi depredations against Norwegians. Hamsun tried to have him remove Josef Terboven from the position of Reichskommissar of Norway. He even asked Hitler to release the Norwegians (including the Norwegian Jews) from the concentration camps, which enraged Hitler. A week after Hitler's death, Hamsun wrote a eulogy for Hitler, saying “He was a warrior, a warrior for mankind, and a prophet of the gospel of justice for all nations.” Following the end of the war, angry crowds burned his books in public in major Norwegian cities and Hamsun was confined for several months in a psychiatric hospital.

Hamsun was forced to undergo a psychiatric examination, which concluded that he had "permanently impaired mental faculties", and on that basis the charges of treason were dropped. Instead, a civil liability case was raised against him, and in 1948 he had to pay a ruinous sum to the Norwegian government of 325,000 kroner for his alleged membership in Nasjonal Samling and for the moral support he gave to the Germans, but was cleared of any direct Nazi affiliation.

Hamsun has been somewhat redeemed since: he was not a Nazi himself, stood up to Hitler in defense of Norwegians, most likely didn't understand what the Nazis were up to, and was punished for his sympathies. Whether he was a member of Nasjonal Samling or not and whether his mental abilities were impaired is a much debated issue even today. Hamsun stated he was never a member of any political party. He wrote his last book Paa giengrodde Stier (On Overgrown Paths) in 1949, a book many take as evidence of his functioning mental capabilities. In it, he harshly criticizes the psychiatrists and the judges, and in his own words proves that he is not mentally ill.

The Danish author Thorkild Hansen investigated the trial and wrote the book The Hamsun Trial (1978), which created a storm in Norway. Among other things Hansen stated: "If you want to meet idiots, go to Norway", as he felt that such treatment of an old man was outrageous. In 1996 the Swedish director Jan Troell based the movie Hamsun on Hansen's book. In Hamsun, the Swedish actor Max von Sydow plays Knut Hamsun; his wife, Marie, is played by the Danish actress Ghita Nørby.