Hungarian born British novelist, journalist, and critic, best known for his novel Darkness at Noon (1940), which reflects his break with the Communist Party, and his ideological rebirth. From 1937 Koestler was one of the main representatives of politically active European authors, whose attacks on the Soviet totalitarianism during the early period of the Cold War separated him from such internationally famous intellectuals as Sartre and Brecht. Since 1956 he focused on mainly in questions of science and mysticism, especially on telepathy and extrasensory perception.

"All great works of literature contain variations and combinations, overt or implied, of such archetypal conflicts inherent in the condition of man, which first occur in the symbols of mythology, and are restated in the particular idiom of each culture and period. All literature, wrote Gerhart Hauptmann, is 'the distant echo of the primitive world behind the veil of words'; and the action of a drama or novel is always the distant echo of some ancestral action behind the veil of the period's costumes and conventions." (in The Act of Creation, 1964)

Arthur Koestler was born in Budapest, the son of Henrik K. Koestler, an industrialist and inventor, and Adele (Jeiteles) Koestler. Arthur was their first and only child. "Everything seems to have gone wrong with my birth: I weighted over ten pounds; my mother's labor lasted two days and almost killed her," he said in his autobiography. "The whole unsavory Freudian Olympus, from Oedipus Rex to Orestes, stood watch at my craddle." Koestler' s parents were Jewish, but later in 1949-50 Koestler "renounced" his religious heritage. As a businessmann Henrik Koestler was unprejudiced – he financed disastrous inventions like the envelope-opening machine and radioactive soap. In 1922 Koestler entered the University of Vienna (1922-26), and became attracted to the Zionist movement. During this period he worked with the revisionist, militant Zionist Vladimir Jabotinsky. Koestler left for the Palestine in 1926 without completing his degree. First he worked as a farm laborer and then as a Jerusalem-based correspondent for German newspapers. In 1929 he was transferred to Paris, a year later to Berlin where he became science editor of Vossische Zeitung and foreign editor of B.Z. am Mittag.

From 1932 to 1938 Koestler was a member of the German Communist Party, but left the party during the Moscow trials. He lived in France in 1932-36, earning his living as a free-lance journalist. In the early 1930s, Koestler travelled to Mount Ararat, Baku, the Afghan frontier, and Turkmenistan (then the Turkmen Soviet Republic), composing propaganda on Soviet progress. In Turkmenistan he met the American poet Langston Hughes, who later portrayed Koestler in his autobiography. While in Paris Koestler edited the anti-Hitler and anti-Stalin weekly Zukunft.

During the Spanish Civil War Koestler was captured by the Franco forces. The author had remained in Malaga after the military commanders had fled, and he actually had no more duties as a correspondent. Koestler spend his time under sentence of death in some kind of mystical passivity. He used the library of the relatively luxurious jail at Seville and went on hunger strikes. It became apparent for the author, that he was an exception among the prisoners –  others were freely killed. In a message three other prisoners, republican militiamen, wrote to him: "Dear comrade foreigner, we three are also condemned to death, and they will shoot us tonight or tomorrow. But you may survive; and if you ever come out you must tell the world about all those who kill us because we want liberty and no Hitler."

"Indeed, the ideal for a well-functioning democratic state is like the ideal for a gentleman's well-cut suit- it is not noticed. For the common people of Britain, Gestapo and concentration camps have approximately the same degree of reality as the monster of Loch Ness. Atrocity propaganda is helpless against this healthy lack of imagination." (in 'A Challenge to 'Knights in Rusty Armor'', The New York Times, February 14, 1943)

Finally the British Foreign Office managed to arrange for Koestler's release. This period he depicted in  Spanish Testament (1937), rewritten as Dialogue with Death (1942). From 1936 to 1939 he was a correspondent for the News Chronicle. Koestler's first book in English, Scum of the Earth, an autobiography, came out in 1941.

The Gladiators (1939) was Koestler's first novel. It dealt with the Spartacus slave revolt in Rome, one of the favorite subjects of leftist writers from ancient history. In October 1939  Koestler was arrested and interned in Le Vernet under the Vichy government.  Nicknamed as the "French Dachau, " it was the most notorious camp, but Koestler managed to gain a privileged position and permission to continue his writing. Harold Nicholson,  deputy minister, and Paul Willert, a diplomat, lobbied for his release and in January 1940 he was back in Paris. Before escaping to England, Koestler enlisted in the French Foreign Legion.

In his new home country, where he was detained for six weeks in Pentonville Prison upon his arrival, Koestler changed his language from German to English. Daphne Hardy, a sculptor and his lover in Paris and wartime London, had translated Darkness at Noon into English. Koestler served in the British Pioneer Corps (1941-42) and after being discharged from the army he was employed by the Ministry of Information and BBC. For a short period he shared an apartment with the critic and literary editor Cyril Connolly and his girlfriend, Lys Lubbock, and the poet and critic Peter Quennell. The aparment belonged to Celia and Mamaine Paget; Mamaine became Koestler's second wife. 

Koestler acquired British citizenship in 1945. He lived in North Wales three years but also traveled between England and the United States. In Suffolk he had a farmhouse. To the philosopher A.J. Ayer, who visited his house in Wales, Koestler confessed that he aspired to become the "Darwin of the 20th century". Later Ayer wrote that Koesler "has proved himself a man of exceptional gifts, but his mind had displayed a religious rather than a scientific bent." Koestler met Sartre in 1946 in Paris, where he socialized not only with Sartre but also with Albert Camus and Simone de Beauvoir, with whom he had a one-night stand. Camus fell in love with Mamaine. When Sartre began making love to Mamaine as a joke, Koestler threw a glass at his head and it smashed against the wall.

Darkness at Noon, published in France under the title Le Zero et l'Infini was there a great success, selling over 400,000 copies, which annoyed the Communists. "I don't believe that my point of view is superior to yours, or yours to mine," Sartre later wrote, but they never became close friends. In his preface to Andre Gorz's The Traitor (tr. 1959) Sartre analyzed Koestler's psychology. Sartre's unofficial secretary told once that Camus got a black eye from Koestler, after they had raced on all fours across the Place Saint-Michel. Camus lost and accused Koestler of cheating. "It is impossible to be friends if you differ about politics!" he once said to Camus, blaiming him and Sartre of trying to compromise with the Soviets. Under the influence of Koestler's personality and his book Le Zero et l'Infini Camus began to reason what is wrong with Communism.

Koestler made his international breakthrough as a writer with Darkness at Noon, which revealed the totalitarian system and the decay of the Russian Revolution. Based partly on writer's own experiences a prisoner and on Stalin's trials, the book depicted the fate of an old idealistic Bolshevik, Rubashov, a victim of Stalin's rule of terror. Rubashov is imprisoned in 1938 and persuaded to confess crimes "against the state", of which he is innocent. In his own mind Rubashov knows he is guilty of working for system, that has cost too much suffering.  "I no longer believe in my own infallibility," he admits. "That is why I am lost." Like Winston Smith in Orwell's Nineteen Eighty-Four (1949), he accepts his fate: a bullet in the back of the neck. Rubashov provided the model for Orwell's hero, who is his parodic dobbelganger.  Darkness at Noon is considered one of the most powerful political fictions of the century. It was adapted for the Broadway stage by Sidney Kingsley in 1951.

Koestler's other works about Stalinism and Communism include The Yogi and the Commissar (1945) and The God That Failed  (1949). "I am told that Koestler's influence among the left-wing intellectuals is great and disturbing, and the origin of many crises de conscience", said the Russian-born British journalist and writer Alexander Werth in his address given at Chatman House in 1945. "I have read through a large part of his book, The Yogi and the Commissar, and I was not impressed." In his memoirs, Arrow in the Blue (1951) and The Invisible Writing (1954), Koestler analyzed his quest for Utopia and his disillusionment with Russian communism. "In the social equation, the value of a single life is nil; in the cosmic equation, it is infinite... Not only communism, but any political movement which implicitly relies on purely utilitarian ethics, must become a victim to the same fatal error. It is a fallacy as naïve as a mathematical teaser, and yet its consequences lead straight to Goya's Disasters, to the reign of the guillotine, the torture chambers of the Inquisition, or the cellars of the Lubianka." (in The Invisible Writing) In 1950 Koestler took a leading part in an international meeting of writers, scholars and scientists in West Berlin, organized as a counteract against Soviet-backed cultural conferences. The Congress for Cultural Freedom was later revealed to be a CIA Cold War operation.

From the 1950s Koestler published scientific and philosophical works. The Sleepwalkers: A History of Man's Changing Vision of the Universe (1959), a best-selling history of early astronomy, prompted the Smithsonian professor of astronomy and history of science, Owen Gingerich, to prove wrong Koestler's claim, that Copernicus' De revolutionibus (1543) was a book that nobody read, "an all time worst seller". Gingerich recorded his decades long odyssey from library to library in the engaging bibliophilic detective story The Book Nobody Read (2004), concluding that Koestler "couldn't have been more mistaken."

For a while Koestler lived in Delaware in the United States with his second wife – his future third wife, Cynthia Jefferies, acted as his secretary. "A gentle, soft, sad woman" described Duncan Fallowell her in his interview of Koestler – the last he granted before his death. The author himself was not at his best, he had a cold, and he answered shortly, except when he was talking about the influence of his books. "Look at this. Did you ever see a magazine called the New Musical Express? It turns out there is a pop group called The Police – I don't know why they are called that, presumably to distinguish them from the punks – and they've made an album of my essay "The Ghost in the Machine." I didn't know anything about it until my clipping agency sent me a review of the record." (in Writers at Work, ed.  George Plimpton, 1986)

In the preface to his book of essays The Trail of the Dinosaur (1955), Koestler declared his literary-political career over. During 1958 and 1959 he travelled to India and Japan, in order to discover whether the East could offer a spiritual aid to the West. For his disappointment, he did not find what he was looking for and reported on his failure in The Lotus and the Robot (1960). Koestler's article about Anglo-American 'drug culture, 'Return Trip to Nirvana' appeared in Sunday Telegraph in 1967 and challenged Aldous Huxley's defence of drugs. He experimented at the University of Michigan at Ann Arbor with psilocybin and combined its effect to his vision to Walt Disney's Fantasia. "I profoundly admire Aldous Huxley, both for his philosophy and uncompromising sincerity. But I disagree with his advocacy of 'the chemical opening of doors into the Other World', and with his belief that drugs can procure 'what Catholic theologians call a gratuitous grace'. Chemically induced hallucinations, delusions and raptures may be frightening or wonderfully gratifying; in either case they are in the nature of confidence tricks played on one's own nervous system."

In the 1970s Koestler was made a Commander of the Order of the British Empire and a Companion of Literature. Facing incurable illness – Parkinson's disease and terminal leukemia – and as a lifelong advocate of euthanasia, Koestler took his own life with his wife, who, however, was perfectly healthy. Koestler died of a drug overdose – his death was reported on March 3, 1983. In her suicide note Cynthia Koestler wrote, "I cannot live without Arthur, despite certain inner resources." Koestler was married three times: to Dorothy Asher (1935-50), Mamaine Paget (1950-52), and Cynthia Jefferies (1965-83). He also had several affairs – but his one one-night stand with Simone de Beauvoir in Paris was for both of them something they did not want to repeat. Noteworthy, Beauvoir described him as rough but not a rapist. Koestler's sister-in-law, Celia Kirwan (née Paget), worked at the IRD, a secretly funded anti-communist propaganda unit attached to the Foreign Office. Without success, George Orwell proposed marriage to  her. Koestler himself also cooperated with IRD.

Throughout his life Koestler had psychic experiences, though he maintained that he was not himself psychic, did not believe in "hidden wise men in Tibet", and never met Gurdjieff or Aleister Crowley. He established The Koestler Foundation, which exists to promote research in parapsychology and other fields. In his will Koestler left his entire property to found a Chair of Parapsychology at the Edinburgh University. Koestler's best-know scientific publications from the 1970s are The Roots of Coincidence (1972), an attempt to provide extrasensory perception with a basis in quantum physics, and The Challenge of Chance: A Mass Experiment in Telepathy and Its Unexpected Outcome (1973), where he related his study of coincidences to the 'synchronicity' hypotheses of Carl Jung and Kammerer, a zoologist wrongly convicted of fraud because he seemed to have discovered an exception to the rule, that acquired characteristics cannot be inherited.

David Cesarani claimed in his book The Homeless Mind (1998), that Koestler raped several women in the 1950s. One of his victims, according to Cesarini, was Jill Craigie, a documentary film director married to the Labor M.P. Michael Foot. Craigie's account had similarities with a scene from Koestler's novel Arrival and Departure (1943). After the publication the book, Koestler's bust sculpted by Daphne Hardy Henrion at the Edinburgh University was removed to safer place to avoid attacks. Koestler's diary entry for that day reads, "Jill Foot – Sunday pubcrawl on Heath." Craigie made her story public in the mid-1990s, at a dinner party for Salman Rushdie.

For further reading: Arthur Koestler by J. Atkins (1956); Chronicles of Conscience: A Study of Arthur Koestler and George Orwell by J. Calder (1968); Arthur Koestler: A Collection of Critical Essays, ed. by M.A. Sperber (1977); Arthur Koestler by S.A. Pearson (1978); Koestler by I. Hamilton (1982); Arthur Koestler by G. Mikes (1983); Arthur Koestler by M. Levene (1984); Living with Koestler with M. Koestler (1985); Arthur Koestle: A Guide to Research (1987); Arthur Koestler: The Homeless Mind by David Cesarani (2000); Koestler: The Literary and Political Odyssey of a Twentieth-Century Skeptic by Michael Scammell (2009) - Paranormal and psychic phenomena, see also: Nostradamus

Selected works:

•  Spanish Testament, 1937 (with an introduction by the Duchess of Atholl; abridged as  Dialogue with Death, 1942)
• The Gladiators, 1939 (translated by Edith Simon)
• Darkness at Noon, 1940 (translated by Daphne Hardy; a play in three acts based on the novel; by Sidney Kingsley, 1952)
  - Pimeää keskellä päivää (suom. Tauno Tainio, 1958)
  - TV film 1955, prod. Showcase Productions, dir. Delbert Mann, written by Robert Alan Aurthur, Sidney Kingsley, starring Lee J. Cobb, Robert Gibbons, Michael Gorrin, Oskar Homolka   
• Scum of the Earth, 1941 (translated by Daphne Hardy)
• Dialogue with Death, 1942 (translated from the Germany by Trevor and Phyllis Blewitt)
• Arrival and Departure, 1943
  - Tuomion päivä (suom. Eino Ismala, 1946)
• Twilight Bar: An Escape in Four Acts, 1945
  - TV play 1966: Drei Tage bis Mitternacht, dir.  Claus Peter Witt, prod. Norddeutscher Rundfunk (NDR), featuring Erwin Wirschaz, Walter Kohut, Susi Nicoletti, Hans-Peter Korff
• The Yogi and the Commissar and Other Essays, 1945
• Thieves in the Night; Chronicle of an Experiment, 1946
• The Challenge of our Time: A Series of Essays, 1948 
  
• The God That Failed: Six Studies in Communism, 1949 (ed.  R. Crossman)
• Promise and Fulfilment: Palestine 1917–1949, 1949
• Insight and Outlook: An Inquiry into the Common Foundations of Science, Art and Social Ethics , 1949
• The Age of Longing, 1951
• Arrow In The Blue: An Autobiography, 1952
• The Invisible Writing, 1954
• The Trail of the Dinosaur and Other Essays, 1955
• Reflections on Hanging, 1956
• The Sleepwalkers: A History of Man's Changing Vision of the Universe, 1959 (with an introd. by Herbert Butterfield; abridged as The Watershed, 1960)
  - Vedenjakajalla: Johannes Keplerin elämäkerta (suom. Reino Tuokko, 1961)
  - TV film 1970: I Measured the Skies, dir.  John Glenister, adaptation by James Brabazon, featuring Richard Vernon as Tycho Brahe and Tony Calvin as Johannes Kepler
• The Lotus and the Robot, 1960
• The Watershed: A Biography of Johannes Kepler, 1960 (foreword by John Durston, illustrated by R. Paul Larkin)
• Control of the Mind, 1961
• Hanged by the Neck: An Exposure of Capital Punishment in England, 1961
• Suicide of a Nation?: An Enquiry into the State of Britain Today 1963 (edited by Arthur Koestler)
  
• The Act of Creation, 1964
• The Ghost in the Machine, 1967
• Drinkers of Infinity: Essays 1955-1967, 1968
• Beyond Reductionism: New Perspectives in the Life Sciences, 1969 (edited by Arthur Koestler & J. R. Smythies)
• The Case of the Midwife Toad, 1971
• The Call-Girls: A Tragi-Comedy with Prologue and Epilogue, 1972
• The Roots of Coincidence, 1972
  - Parapsykologiaa vai yhteensattumaa (suom. Matti Kannosto, 1973)
• The Lion and the Ostrich, 1973
• The Challenge of Chance: Experiments and Speculations, 1973 (with Alister Hardy and Robert Harvie)
• The Heel of Achilles: Essays 1968-1973, 1974
• The Thirteenth Tribe: The Khazar Empire and Its Heritage, 1976
• Life After Death, 1976 (co-ed.)
  - Mitä elämän jälkeen? (suom. Pekka Haapakoski, 1977)
• Twentieth Century Views: A Collection of Critical Essays, 1977
  
• Janus: A Summing Up, 1978
• Bricks to Babel: Selected Writings with Comments by the Author, 1980
• Kaleidoscope: Essays from Drinkers of Infinity, and The Heel of Achilles and Later Pieces and Stories, 1981
  
• Stranger on the Square, 1984 (edited by Harold Harris)