Sapper was born Herman Cyril McNeile in Bodmin, Cornwall, England, on September 28, 1888. He was the son of a naval officer, Captain Malcolm McNeile, who was once governor of the Royal Naval Prison at Lewes. His mother was Christiana Mary Sloggett. Educated at Cheltenham College, McNeile went on to officer school at the Royal Military Academy in Woolwich. In 1907, he joined the Royal Engineers (from which he adopted the pen name Sapper, a slang word for a military engineer). Promoted to captain in 1914, McNeile served in World War I from 1914 to 1918 and was awarded the Military Cross.
In 1919, McNeile retired from the service with the rank of lieutenant colonel. Not wanting to take up a mundane profession, he began writing for a living. He had already published several books and articles on the war, but it was not until 1920, when Bull-Dog Drummond: The Adventures of a Demobilized Officer Who Found Peace Dull appeared, that he had his first success. This success was so great that a dramatized version of the book quickly went on the boards the following year (with Gerald du Maurier playing Drummond) and later played in New York.
McNeile reaped the rewards of his lucrative invention, and new Drummond books appeared almost annually. When the first film with the Drummond character was released in the early 1920’s, another source of income was opened, and it proved to be a rich one. Some twenty films later, Drummond had been played by Ronald Colman, Ralph Richardson, John Howard, Tom Conway, Ron Randell, and even Walter Pidgeon. As a result of these films, and the books, McNeile became a wealthy man.
McNeile was married to Violet Baird, the daughter of Scottish boxing patron Arthur Sholto Douglas, and had two sons. Aside from his very successful career as a writer, McNeile lived a quiet life. However, he had not escaped from his experiences in the Great War: He died, from complications resulting from his war injuries, on August 14, 1937.