John Rowland Mallard OBE FRSE FREng (14 January 1927 – 25 February 2021) was an English physicist and professor of Medical Physics at the University of Aberdeen from 1965 until his retirement in 1992. He was known for setting up and leading the team that developed the first magnetic resonance imaging (MRI) full body scanner and, in particular, positron emission tomography (PET). He was born in Kingsthorpe, Northampton, England.