Sir William John Ritchie Simpson CMG (27 April 1855 – 20 September 1931) was a Scottish physician and specialist in tropical medicine.

[2][a] Simpson moved to Kent, where he was Medical Officer for a district of the Dover poor law union and a public vaccinator.

[1] Simpson returned to London and in 1898 became professor of hygiene and lecturer in tropical medicine at King's College.

[1] The Roan Antelope Copper Mine in Northern Rhodesia (now Zambia) experienced a high death rate during construction between 1927 and 1930.

[6] In 1929 the managers of the mining company in London arranged for the Ross Institute for Tropical Diseases to send an expedition led by Simpson to find what was causing the deaths.

[4] His biographer writes that "Simpson was a man of great industry and an inflexible purpose that sometimes led to clashes with his associates.

"[4] Simpson sometimes ignored local knowledge and cultural concerns, and created resistance to his sanitary reforms through his insensitivity.

His solution was often to destroy large parts of colonial cities and to rebuild them according to current theories of sanitation.