William Miller Macmillan (1 October 1885 in Aberdeen, Scotland – 23 October 1974 in Long Wittenham, Berkshire, England) is regarded as a founder of the liberal school of South African historiography and as a forerunner of the radical school of historiography that emerged in the 1970s. He was also a critic of colonial rule and an early advocate of self-government for colonial territories in Africa and of what became known as development aid.