Thomas was born in Wales, the son of a coal miner, and his early life was spent in the Gwendraeth Valley in South Wales; throughout his life he remained passionately committed to his native land, its language and literature. He was both an undergraduate and postgraduate student at Swansea University and after a brief postdoctoral period at the Atomic Weapons Establishment, Aldermaston, he was appointed a Lecturer at Bangor University and subsequently Professor at Aberystwyth University. In 1978 he moved to the University of Cambridge as Professor of Physical Chemistry and subsequently to London, where he was Director of the Royal Institution from 1986–1991 — an ideal role for him as it allowed him to combine his creativity as a scientist with his deep interest in the history of science and his skills as a lecturer and communicator of science. In the early 1990s he took up a senior appointment in the University of Wales before returning to Cambridge as Master of Peterhouse College. More details of his remarkable career can be found in several eloquent obituaries and tributes, for example ref. 1. Our focus here will be on his wide-ranging and highly influential scientific contributions.