Born on 15 June 1870 at Long Compton, Warwickshire, fifth child and second son of Finlay Dun of Edinburgh, land agent, and his wife, *née* Craig. Dun was educated at Loretto School and Edinburgh University, where he graduated with second-class honours in the medical school in 1893 and was Gunning Victoria jubilee scholar in pathology in 1894. He later studied at Berlin and Bern, and served as house surgeon and house physician in the Edinburgh Royal Infirmary. Dun was appointed assistant lecturer and senior demonstrator of anatomy at Liverpool University College, and was later elected assistant surgeon to the Stanley Hospital. His interests turning to the surgery of children, he was appointed in 1900 to the staff of the Children's Infirmary, which became the Royal Liverpool Children's Hospital, and retired as consulting surgeon in 1932. He was also consulting surgeon to the Liverpool Hospital for Children at Leasowe and to the West Kirby Convalescent Home for Children. He was particularly interested in the cranial surgery of children. He was for several years chairman of the Liverpool Hospitals' Staffs Association and was president of the Liverpool Medical Institution in 1925. Dun saw active service in the South African war, and received a commission as captain in the RAMC(T) on 7 January 1912. He was promoted brevet-major on 1 January 1918 and subsequently lieutenant-colonel. He was a man of broad, thick-set figure, who used his large hands with exquisite neatness and gentleness, and veiled his strength under a quiet and courteous manner. Dun married on 2 July 1907 H Louise Bowring, who survived him with three daughters. He died on 31 January 1941 at Fitz Manor near Shrewsbury.