Hugh Redwald Trevor-Roper, Baron Dacre of Glanton, FBA (15 January 1914 – 26 January 2003) was an English historian. He was Regius Professor of Modern History at the University of Oxford.

Trevor-Roper was a polemicist and essayist on a range of historical topics, but particularly England in the 16th and 17th centuries and Nazi Germany. According to John Philipps Kenyon, "some of [Trevor-Roper's] short essays have affected the way we think about the past more than other men's books". Richard Davenport-Hines and Adam Sisman wrote that "The bulk of his publications is formidable ... Some of his essays are of Victorian length. All of them reduce large subjects to their essence. Many of them ... have lastingly transformed their fields." Conversely, Sisman wrote: "the mark of a great historian is that he writes great books, on the subject which he has made his own. By this exacting standard Hugh failed."

In 1945, British intelligence tasked Trevor-Roper with ascertaining the facts about Adolf Hitler's demise. From interviews with a range of witnesses and study of surviving documents, he concluded in The Last Days of Hitler (1947) that Hitler was dead and had not escaped Berlin.

In 1983, Trevor-Roper's reputation was "severely damaged" when he authenticated the Hitler Diaries shortly before they were shown to be forgeries.

Trevor-Roper was born at Glanton, Northumberland, England, the son of Kathleen Elizabeth Davidson (died 1964) and Bertie William Edward Trevor-Roper (1885–1978), a doctor, descended from Henry Roper, 8th Baron Teynham and second husband of Anne, 16th Baroness Dacre. Trevor-Roper "enjoyed (but not too seriously) ... that he was a collateral descendant of William Roper, the son-in-law and biographer of Sir Thomas More ... as a boy he was aware that only a dozen lives (several of them those of elderly bachelors) separated him from inheriting the Teynham peerage."

Trevor-Roper's brother, Patrick, became a leading eye surgeon and gay rights activist. Trevor-Roper was educated at Belhaven Hill School, Charterhouse, and Christ Church, Oxford, where he read first Classics (Literae Humaniores) and then Modern History. He got a first-class degree in Classical Moderations in 1934 and won the Craven, the Ireland, and the Hertford scholarships in Classics. Initially, both he and his brother intended to make their careers in the Classics, but Hugh became bored with what he regarded as the pedantic technical aspects of the classics course at Oxford and switched to history, where he obtained first-class honours in 1936. Whilst at Oxford, he was a member of the exclusive Stubbs Society and was initiated as a Freemason in the Apollo University Lodge.

In 1937, he moved from Christ Church to Merton College, Oxford to become a research fellow. His first book was a 1940 biography of Archbishop William Laud, in which he challenged many of the prevailing perceptions surrounding Laud.

Trevor-Roper was a member of the University of Oxford's Officer Training Corps, reaching the rank of officer cadet corporal. On 28 February 1939, he was commissioned in the British Army as a second lieutenant with seniority in that rank from 1 October 1938, and attached to the cavalry unit of the Oxford University Contingent of the OTC. On 15 July 1940, he was promoted to war substantive lieutenant and transferred to the Intelligence Corps, Territorial Army.