Before becoming a full professor, J.R.R. Tolkien specialized academically in Anglo-Saxon at Oxford University.
Tolkien was appointed Rawlinson and Bosworth Professor of Anglo-Saxon at Oxford in 1925. Anglo-Saxon, also called Old English, was the language used in England before the Norman Conquest and is preserved in works such as Beowulf.
His scholarship in language and medieval literature strongly influenced his creative writing. He drew on Old English words, names, poetic traditions, and heroic themes when developing parts of Middle-earth. His famous public lecture on Beowulf, later published as “Beowulf: The Monsters and the Critics,” helped reshape modern academic discussion of the poem.
Tolkien later became Merton Professor of English Language and Literature. That later post does not erase his earlier specialty, and “Old English” is the modern linguistic name most readers will encounter for Anglo-Saxon. Old Norse was also important to his interests, but it was not the answer to this Oxford appointment question.