John Percy Lockhart-Mummery FRCS, was a British surgeon at St Mark's Hospital, London, who devised a classification of rectal cancer and described familial polyposis which led to the formation of the polyposis registry. He was the author of several books, including Diseases of the Rectum and Colon and their Surgical Treatment (1923) and The Origin of Cancer (1934). His work on colorectal surgery earned him the nickname "King Rectum".

St Mark's Hospital, The National Bowel Hospital is a hospital in Park Royal, Greater London, England. Managed by London North West University Healthcare NHS Trust, it is the only hospital in the world to specialise entirely in intestinal and colorectal medicine and is a national and international referral centre for intestinal and colorectal disorders. It is the only hospital in the UK, and one of only 14 worldwide, to be recognised as a centre of excellence by the World Organisation of Digestive Endoscopy.