Henry Cyril MacNeile
According to Wikipedia: "Herman Cyril McNeile, MC, commonly known as Cyril McNeile and publishing under the name H. C. McNeile or the pseudonym Sapper, was a British soldier and author. Drawing on his experiences in the trenches during the First World War, he started writing short stories and getting them published in the Daily Mail. As serving officers in the British Army were not permitted to publish under their own names, he was given the pen name "Sapper" by Lord Northcliffe, the owner of the Daily Mail; the nickname was based on that of his corps, the Royal Engineers.
After the war McNeile left the army and continued writing, although he changed from war stories to thrillers. In 1920 he published Bulldog Drummond, whose eponymous hero became his best-known creation. The character was based on McNeile himself, on his friend Gerard Fairlie and on English gentlemen generally. McNeile wrote ten Bulldog Drummond novels, as well as three plays and a screenplay."