John M. Stewart was Emeritus Reader in Gravitational Physics at the University of Cambridge, and a Life Fellow at King's College, Cambridge before his death in 2016. He was the author of 'Non-equilibrium Relativistic Kinetic Theory (Springer, 1971) and 'Advanced General Relativity' (Cambridge, 1991), and he translated and edited Hans Stephani's 'General Relativity' (Cambridge, 1990).