David Crook was a British-born Communist ideologue, activist and spy, long resident in China. A committed Marxist from 1931, he joined the International Brigades during the Spanish Civil War (1936–39), then was recruited by the KGB, the Soviet secret police, and was sent to China during the Second Sino-Japanese War (1937–45). There he met and married his wife, Isabel, a teacher and social activist. The couple stayed in China after 1949 to teach English