Dominic Welsh

James Anthony Dominic Welsh, known professionally as D. J. A. Welsh (1938 to 2023), was an English mathematician and professor in Oxford University's Mathematical Institute. He was an expert in matroid theory, the computational complexity of combinatorial enumeration problems, percolation theory and cryptography. He took his doctorate at Oxford under John Hammersley, worked as a researcher at Bell Laboratories, and joined the Mathematical Institute in 1963, becoming a fellow of Merton College in 1966. He chaired the British Combinatorial Committee from 1983 to 1987, was given a personal chair in 1992 and retired in 2005, having supervised 28 doctoral students. His books include Matroid Theory, Probability: An Introduction with Geoffrey Grimmett, and Codes and Cryptography. The Russo-Seymour-Welsh estimate in percolation theory is partly named after him.