1905-1983. Hungarian-English author of such books as: The Act of Creation, The Sleepwalkers : A History of Man's Changing Vision of the Universe, The Ghost in the Machine, The God That Failed, and the 1941 anti-Stalinist Darkness at Noon (which is on the Modern Library's 100 Best Books list). Also a political activist and a social philosopher.

One night Koestler got drunk with his wife,Albert Camus & Jean Paul Sartre. Sartre was flirting with Koestler's wife so Koestler decided to throw a glass at his head, which missed due to his drunken state. Later on that night Koestler tried to knock out Camus.
Amusing trivia from Albert Camus a Biography by Herbert Lotterman

Koestler also wrote The Roots of Coincidence, The Case of the Midwife Toad, The Heel of Achilles, The Thirteenth Tribe, The Call-Girls.

Arthur Koestler was a rapist.

One of the women he raped was the British film director Jill Craigie, in 1951. She was the wife of Michael Foot, who was to become leader of the Labour Party; she concealed it from her husband for forty years: it was publicly revealed in a 1998 biography of Koestler by David Cesarini (The Homeless Mind). The victims said they felt unable to report his beatings and rapes because he was such a "respected" figure.

The novelist Frederick Raphael caused a storm by trying to defend Koestler's reputation. He says Craigie invited the rape by asking a known serial abuser in for dinner. (She was reluctant to but he was drunk, and a friend of her husband's, and insisted on an omelette.)

He also believed in parapsychology and endowed a chair in it at Edinburgh University. A bust of him here was removed after the revelation of his behaviour.

He and his wife Cynthia died in a suicide pact.