Robert Fitzroy 'Roy' Foster (born 16 January 1949), publishing as R. F. Foster, is an Irish historian and academic. He was the Carroll Professor of Irish History from 1991 until 2016 at Hertford College, Oxford.
Foster was born on 16 January 1949 in Waterford, to two teachers: Betty Foster (née Fitzroy), a primary teacher, and 'Fef' (Ernest) Foster, a teacher of Irish. His father, Fef, was a native of Drung, a tiny hamlet and parish located between Cavan Town and Cootehill in County Cavan. Roy attended Newtown School in Waterford, a multi-denominational school that was founded as a Quaker school in the late 18th century. He won a scholarship to attend St. Andrew's School in Delaware for a year before reading history at Trinity College Dublin. He was awarded an M.A. and PhD by Trinity College, where he was taught by T. W. Moody and F. S. L. Lyons, and was elected a scholar in History and Political Science in 1969.
Prior to his appointment to the Carroll professorship, he was Professor of Modern British History at Birkbeck, University of London, University of London, and held visiting fellowships at St Antony's College, Oxford, the Institute for Advanced Study, Princeton, and Princeton University. Based in London as well as at Hertford College in Oxford, Foster visits Ireland frequently.
His work is generally published under the name R. F. Foster.
He has written early biographies of Charles Stewart Parnell and Lord Randolph Churchill, edited The Oxford History of Ireland (1989), and written Modern Ireland: 1600-1972 (1988) and several books of essays. Foster produced a much-acclaimed two-part biography of W. B. Yeats, which was awarded the James Tait Black Memorial Prize, and collaborated with Fintan Cullen on a National Portrait Gallery exhibition, 'Conquering England: the Irish in Victorian London'. Seamus Deane wrote a review in The Irish Times of 27 September 2003 quoting W. B. Yeats as saying "My glory was that I had such friends". Deane then suggests Yeats was also lucky to have such a biographer as Foster.
He has been married to the novelist and critic Aisling Foster (née O'Conor Donelan) since 1972 and they have two children.
In 1989, he was elected Fellow of the British Academy (FBA)  and in 2010 he was elected an Honorary Member of the Royal Irish Academy (Hon. MRIA). He is also an elected Fellow of the Royal Society of Literature (FRSL), and a Fellow of the Royal Historical Society (FRHistS).