Arthur Koestler CBE (UK: /ˈkɜːstlər/, US: /ˈkɛst-/; German: [ˈkœstlɐ]; Hungarian: Kösztler Artúr; 5 September 1905 – 1 March 1983) was a Hungarian-born author and journalist. Koestler was born in Budapest and, apart from his early school years, was educated in Austria. In 1931, Koestler joined the Communist Party of Germany, but he resigned in 1938 after becoming disillusioned with Stalinism.

Having moved to Britain in 1940, he published his novel Darkness at Noon, an anti-totalitarian work that gained him international fame. Over the next 43 years, Koestler espoused many political causes and wrote novels, memoirs, biographies, and numerous essays. In 1949, Koestler began secretly working with a British Cold War anti-communist propaganda department known as the Information Research Department (IRD), which would republish and distribute many of his works, and also fund his activities.[2][3] In 1968, he was awarded the Sonning Prize "for [his] outstanding contribution to European culture". In 1972, he was made a Commander of the Order of the British Empire (CBE).

In 1976, he was diagnosed with Parkinson's disease and in 1979 with terminal leukaemia.[4][5] On 1 March 1983, Koestler and his wife Cynthia committed suicide together at their London home by swallowing lethal quantities of barbiturate-based Tuinal capsules.