William Cullen followed almost every avenue open to him in his medical career. As a general practitioner, surgeon and lecturer at both Glasgow and Edinburgh universities, he specialised in chemistry, botany and surgery. He gained a reputation as the pre-eminent Scottish doctor of his generation, which in 1773 won him the prestigious chair of the practice of medicine at Edinburgh’s medical school. In addition to his own practice, Cullen ran an extensive postal consultation service. At the height of his professional fame, he gave medical advice in response to over 150 letters a year, advising on lifestyle, diet and various forms of medication. This portrait is one of several versions of the same painting. An earlier one, also by Cochran, is owned by the University of Glasgow.