Sir John McGregor Hill, FRS, FREng (21 February 1921 – 14 January 2008) was a British nuclear physicist who was chairman of the UK Atomic Energy Authority for 14 years.
He then served in the Royal Air Force Radar Branch during the Second World War (1941–1945) after which he carried out research into the life span of short-lived radio nuclei at the Cavendish Laboratory, Cambridge and was awarded a Ph.D.
He worked on commissioning Britain's first production nuclear reactors, the Windscale Piles, designed to produce plutonium for military purposes.
When the emphasis changed to the production of nuclear power he became manager of the Production Group relocated at Risley, Cheshire, overseeing the uranium diffusion plan at Capenhurst in Cheshire, the fuel manufacturing plant at Springfields near Preston, the reprocessing plant at Windscale and the power-generating reactors at Calder Hall in Cumbria and Chapelcross, near Annan.
In 1964 he was appointed to the main board of the UK Atomic Energy Authority, rising rapidly to succeed the first chairman, Lord Penney, in 1967, a post he held until 1981.