Ronald Arbuthnott Knox (17 February 1888 – 24 August 1957) was an English Catholic priest, theologian, author, and radio broadcaster. Educated at Eton and Balliol College, Oxford, where he earned a high reputation as a classicist, Knox was ordained as a priest of the Church of England in 1912. He was a fellow and chaplain of Trinity College, Oxford until he resigned from those positions following his conversion to Catholicism in 1917. Knox became a Catholic priest in 1918, continuing in that capacity his scholarly and literary work.

Knox served as Catholic chaplain at the University of Oxford from 1926 to 1939. He completed the "Knox Bible", a new English translation of the Latin Vulgate Bible that was used in Catholic services during the 1960s and 1970s. In 1951, Pope Pius XII appointed Knox protonotary apostolic ad instar, which entitled Knox to the honorific "monsignor".

Knox published extensively on religious, philosophical, and literary subjects. He also produced several popular works of detective fiction. He is remembered for his "Ten Commandments" for detective stories, which sought to codify a form of crime fiction in which the reader may participate by attempting to find a solution to the mystery before the fictional detective reveals it.

Ronald Knox was born into an Anglican family in Kibworth, Leicestershire. His father was the Rev. Edmund Arbuthnott Knox, who later became Bishop of Manchester in the Church of England and who was related to the 8th Viscount of Arbuthnott. Ronald's maternal grandfather was Valpy French, the first Anglican Bishop of Lahore in what was then part of the British Raj. Both Edmund Knox and Valpy French were prominent Evangelical Anglicans.

Ronald was educated at Eaton House School in London and Summer Fields School in Oxford. In 1900 he entered Eton College as first King's Scholar. He enjoyed great academic and social success at Eton, where he was selected for membership in the Eton Society ("Pop") and became captain of the school. He also began to cultivate an interest in Anglo-Catholicism, which put him increasingly at odds with his own family's Evangelical tradition. At age 17, he privately vowed to remain celibate for life.

In 1904 Ronald proceeded to Balliol College, Oxford as the first classics scholar. He won several other scholarships and prizes during his time there: the Hertford Scholarship in 1907; the Craven and Ireland scholarships, the Gaisford Prize for Greek Verse Composition in 1908, and the Chancellor's Prize for Latin Verse Composition in 1910. At Oxford, Knox joined Maurice Child's fashionable "set", which was strongly identified with Anglo-Catholicism.^{[citation needed]}

In 1910, Knox was elected a fellow of Trinity College, Oxford. As he was not expected to begin tutorials until 1911, Knox then accepted the job of private tutor to Harold Macmillan, the brother of a friend from Eton, who was at the time preparing to apply for a scholarship to Balliol. However, Macmillan's mother soon dismissed Knox, after Knox refused to follow her instructions not to discuss religion with Harold.

Knox was ordained an Anglican priest in 1912 and was appointed chaplain of Trinity College. During World War I, he served in military intelligence for the British Armed Forces. In 1915, Cyril Alington, the headmaster of Shrewsbury School, invited Knox to join the teaching staff. Knox was long remembered at Shrewsbury as the highly dedicated and entertaining form master of Vb.