John Cournos (born Иван Григорьевич Коршун, Ivan Grigorievich Korshun, 6 March 1881 – 27 August 1966), a writer of Russian-Jewish background, was born in Kiev, Russian Empire, whence his family emigrated when he was aged 10. During the 1910s and 1920s, he lived in Britain, where his literary career started. He later emigrated to the USA, where he spent the rest of his life.
He was one of the Imagist poets, but is better known for his novels, short stories, essays and criticism, and as a translator of Russian literature. He used the pseudonym John Courtney. He also wrote for The Philadelphia Record under the pseudonym "Gorky."
Later in life he married Helen Kestner (1893–1960), who was also an author, under the pseudonym Sybil Norton. However, he is probably best known for his unhappy affair with Dorothy L. Sayers, fictionalized by Sayers in the detective book Strong Poison (1930) and by Cournos himself in The Devil Is an English Gentleman (1932).