(William) Denis Johnston (18 June 1901 – 8 August 1984) was an Irish writer. Born in Dublin, he wrote mostly plays, but also works of literary criticism, a book-length biographical essay of Jonathan Swift, a memoir and an eccentric work on cosmology and philosophy. He also worked as a war correspondent, and as both a radio and television producer for the BBC. His first play, The Old Lady Says "No!", helped establish the worldwide reputation of the Dublin Gate Theatre; his second, The Moon in the Yellow River, has been performed around the globe in numerous productions featuring such actors as Jack Hawkins, Claude Rains and Errol Flynn, although not all in the same production. He played a role in the 1935 film version of John Millington Synge's Riders to the Sea.
Johnston was a protégé of WB Yeats and Shaw, and had a stormy friendship with Seán O'Casey. He was a pioneer of television and war reporting. He worked as a lawyer in the 1920s and 1930s before joining the BBC as a writer and producer, first in radio and then in the fledgling television service.
In 1939 he produced two plays by Irish playwright Teresa Deevy for BBC television, these were "King of Spain's Daughtee" and "In search of Valour"
During the Second World War he served as a BBC war correspondent, reporting from El Alamein to Buchenwald. For this he was awarded an OBE, a Mentioned in Despatches and the Yugoslav Partisans Medal. He then became Director of Programmes for the television service.