J.R.R. Tolkien held his university professorship in Oxford.
Tolkien spent much of his academic career at the University of Oxford, where he studied languages and literature, taught students, and conducted influential research in philology. He became Rawlinson and Bosworth Professor of Anglo-Saxon in 1925 and Merton Professor of English Language and Literature in 1945.
His academic interests strongly influenced his fiction. He studied Old English, Middle English, Norse, Welsh, and other languages and traditions, and he drew on those materials when creating the histories, names, and languages of Middle-earth.
The answer is sometimes confused with Cambridge because Tolkien’s work was important to British academic culture generally. However, his principal university appointments were at Oxford. He also belonged to literary circles there, including the informal group known as the Inklings, whose members discussed and read works in progress.