Gustav Regler (25 May 1898 in Merzig – 14 January 1963 in New Delhi) - was a German Socialist novelist. He served in the German Infantry during the First World War, and was seriosuly injured; he joined the Communist Party, and spent time in the USSR. He later served as political commissar of the XII International Brigade during the Spanish Civil War. Whilst in Spain he befriended Ernest Hemingway, and was wounded at the Battle of Guadalajara.

As a Communist, he was long time friend of Arthur Koestler, first in Berlin, then Paris and during the Spanish Civil War. Regler's books were banned in the Third Reich.

He wrote about his Spanish experiences in his novel The Great Crusade (New York, 1940), introduced by Ernest Hemingway, translated by Whittaker Chambers. His memoirs were published as The Owl of Minerva in London in 1959. TIME magazine called him the German "Malraux."