William Algernon Churchill (1865 – 23 December 1947) was an art historian and British diplomat.
He was born in Algiers the son of Henry Adrian Churchill (1828–1886) who was an archaeologist and British diplomat, and Maria Braniefska (b. Warsaw 1839?
Three of his four brothers, Harry Lionel (1860–1924), Sidney John Alexander (1862–1924), and George Percy (1876–1973) were also diplomats.
His three sons served in the British Armed Forces during World War II – Walter becoming an ace during the Battle of Britain while Peter and Oliver each served in the Special Operations Executive – and all three were highly decorated, each being awarded the Distinguished Service Order and also a second high-level medal of gallantry.
With illustrations and 578 facsimiles of watermarks.In 1936 he donated a large collection of dated watermarks, ranging from the 15th to the 19th centuries, to the Department of Manuscripts at the British Museum.