Herbert Edward John Cowdrey (29 November 1926 – 4 December 2009), published under H. E. J. Cowdrey, known as John Cowdrey, was a British historian of the Middle Ages and a chaplain in the Church of England. He was elected priest of St Edmund Hall, University of Oxford, in 1956. He resigned the chaplaincy in 1976, but continued to teach medieval history there until 1994, when he retired and was elected emeritus fellow. He was also a Fellow of the British Academy. A leading expert on the Gregorian reforms, his most important work is the monograph Pope Gregory VII, 1073–1085, considered a masterpiece "unlikely to be surpassed".
Born in Basingstoke, Cowdrey attended Queen Mary's School for Boys there from 1937 until 1943, when he won a scholarship to Trinity College, Oxford. At that time, he considered himself an atheist. Drafted into the service because of World War II, he chose to join the Royal Navy in1944. He served aboard HMS Mauritius in the eastern Mediterranean from 1945 to 1947. He arrived before the war was over, but saw no action. On 22 October 1946, he was in one of the magazines during the second Corfu Channel incident, when Mauritius and her flotilla passed through an unexpected minefield off Albania. After his stint in the navy, Cowdrey visited Palestine during the last year of the British mandate.
After returning to Oxford in 1947, Cowdrey studied modern (post-1760) history and theology (under Austin Farrer). He first began research into the medieval papacy and Pope Gregory VII during his theological studies. He also learned biblical Hebrew and ancient Greek, in addition to the modern languages he already knew (English, French, German and Italian). In 1953, he took holy orders at St Stephen's House, Oxford, a High Church seminary, where he also taught Old Testament and theology until 1956, when he took up the chaplaincy at St Edmund Hall. In 1957, St Edmund Hall received new statutes, becoming a full college, and Cowdrey was thus one of the founding fellows.