Ronald Buchanan McCallum (28 August 1898, Paisley, Renfrewshire – 18 May 1973, Letcombe Regis, Berkshire) was a British historian. He was a fellow (and later Master) of Pembroke College, Oxford, where he taught modern history and politics and was a member of J. R. R. Tolkien's Inklings. McCallum was also the creator of the term psephology (statistical analysis of elections).
The fourth and youngest son of Andrew Fischer McCallum, a master dyer, and his wife, Catherine Buchanan Gibson, he was educated at Paisley Grammar School and Trinity College, Glenalmond. During the First World War, he served for two years between 1917 and 1919 as a member of the labour corps of the British expeditionary force in France.
Returning to Britain, he obtained a place at Worcester College, Oxford, where he read history and took his degree with first class honours in 1922.
After spending a year at Princeton University in 1922 and 1923, he became lecturer in history at Glasgow University. In 1925, Pembroke College, Oxford, elected him a fellow and tutor in history and was a member of the Senior Common Room with R.G. Collingwood and Tolkien. He was a tutor for several generations of undergraduates in British history and political institutions, including an influential seminar on British parliamentary procedure. One of his most famous pupils was the Rhodes Scholar and future American Senator J. William Fulbright. Elected to several college offices over the next thirty years, he became Master of Pembroke College in 1955.