John Keith Stuart McKay, 1939–2022

Abstract John McKay was a pioneer in computational group theory who is celebrated for the discovery of several unexpected relations between disparate fields of mathematics. He is perhaps best known for his role in the discovery of Monstrous Moonshine, a mathematical connection between the largest sporadic simple group in finite group theory (the Monster) and modular functions in number theory and analysis. Other remarkable contributions are the McKay Correspondence, which relates affine simply laced Dynkin diagrams with the discrete subgroups of SU(2), and the McKay Conjecture connecting the numbers of characters and normalisers in the representation theory of finite groups. McKay grew up in Kent outside London, attended Dulwich College and the University of Manchester and went on to do his PhD at the University of Edinburgh. After a visiting professorship at CalTech, he moved to McGill University and subsequently to Concordia University, both in Montreal, Canada, where he remained for the rest of his life. John was a kind and gentle man with broad interests and knowledge and a great ability to bring mathematicians and mathematical ideas together. He is remembered with fondness by all who knew him.