Margaret Olwen MacMillan CC CH (born 23 December 1943) is a Canadian historian and professor at the University of Oxford. She is former provost of Trinity College, Toronto and professor of history at the University of Toronto and previously at Ryerson University. Macmillan is an expert on history and international relations. She is a great-granddaughter of former British Prime Minister David Lloyd George. Professor MacMillan was the 2018 Reith lecturer, giving five lectures across the globe on the theme of war under the title The Mark of Cain, the tour taking in London, York, Beirut, Belfast and Ottawa.