Sir John Meurig Thomas (15 December 193213 November 2020), also known as JMT, was a Welsh scientist, educator, university administrator, and historian of science primarily known for his work on heterogeneous catalysis, solid-state chemistry, and surface and materials science. He was one of the founders of solid-state chemistry, starting with his work at the University of Wales, Bangor, in 1958 when he investigated the various ways in which dislocations influence the chemical, electronic and excitonic properties of a range of solids. He was one of the first to exploit electron microscopy as a chemical tool, especially to deduce active-site reactivities from the surface topography of many minerals and crystal hydrates. At the University of Aberystwyth (1969–1978) he elucidated the surface chemistry of diamond, clay minerals, metals and intercalates by pioneering UV and X-ray photoelectron spectroscopy. He also initiated the field of crystal engineering of organic molecules. As head of physical chemistry department at the University of Cambridge (1978–1986), then a separate department to chemistry, he used magic-angle-spinning NMR and high-resolution electron microscopy to characterize and determine the structures of zeolites and other nanoporous catalysts. As Fullerian Professor and Director of the Royal Institution and of the Davy–Faraday Research Laboratory, he utilized synchrotron radiation to characterize, in situ, new catalysts designed for green chemistry and clean technology. He was the recipient of many national and international awards; and, for his contribution to geochemistry, the mineral meurigite was named in his honour. He was Master of Peterhouse, University of Cambridge (1993–2002), and was knighted in 1991 "for services to chemistry and the popularisation of science". Thomas authored more than 1200 scientific articles and several books, including Michael Faraday and the Royal Institution: The Genius of Man and Place (1991), Principles and Practice of Heterogeneous Catalysis (with W. John Thomas, 1997, 2014), and Design and Applications of Single-Site Heterogeneous Catalysts: Contributions to Green Chemistry, Clean Technology and Sustainability (2012). Biography Early life and education Thomas was born and brought up in the Gwendraeth Valley, Carmarthenshire, Wales, near the mining town of Llanelli, where his father and brother were miners. Thomas earned a BSc degree from the University College of Wales, Swansea (later Swansea University) in 1954. He earned a PhD from Queen Mary College (later Queen Mary University of London) in 1958, working with Keble W. Sykes. Personal life In 1959, Thomas married Margaret Edwards with whom he had two daughters, Lisa and