Lieutenant-General Sir William Boog Leishman, KCB, KCMG, FRS (/ˈliːʃmən/, 6 November 1865 – 2 June 1926) was a Scottish pathologist and British Army medical officer.

In 1900 he was made Assistant Professor of Pathology in the Army Medical School, and described a method of staining blood for malaria and other parasites—a modification and simplification of the existing Romanowsky method using a compound of methylene blue and eosin, which became known as Leishman's stain.

In 1901, while examining pathologic specimens of a spleen from a patient who had died of kala azar (now called "visceral leishmaniasis"), he observed oval bodies and published his account of them in 1903.

He was president of the Royal Society of Tropical Medicine and Hygiene in 1911–1912 and Director General of the Army Medical Services from 1923 to 1926.

Twenty-three names of public health and tropical medicine pioneers were chosen to feature on the School building in Keppel Street when it was constructed in 1926.