Dominic Welsh, 1938–2023

Dominic Welsh was born in Port Talbot on 29 August 1938, the eldest child in a family of educators, and died in Oxford on 30 November 2023. He was the first student from his school to attend the University of Oxford, where he remained for the rest of his life as a Fellow of Merton College and a Professor of the University. He combined excellence as tutor and supervisor over nearly 40 years with a distinguished research record in probability and discrete mathematics, where he excelled in both original and expository work. With his DPhil supervisor John Hammersley, he introduced first-passage percolation, and in so doing formulated and proved the first subadditive ergodic theorem. His is the ‘W’ in the ‘RSW’ method that is now central to the theory of random planar media. He was a pioneer in matroid theory with numerous significant results and conjectures, and his monograph has been influential. He worked on computational complexity and particularly the complexity of computing the Tutte polynomial. Throughout his career, he inspired generations of undergraduates and postgraduates, and through his personal enthusiasm and warmth he helped develop a community of scholars in aspects of combinatorics who remember him with love and respect.