At which university did J.R.R. Tolkien teach before returning to Oxford?

Before returning to Oxford, J.R.R. Tolkien taught at the University of Leeds.

Tolkien became a professor of English language at Leeds in 1920, after working on the Oxford English Dictionary. He remained there until 1925, when he moved back to Oxford after being appointed Rawlinson and Bosworth Professor of Anglo-Saxon at Pembroke College.

His Leeds period was academically important. He taught subjects connected with Old and Middle English and worked with E. V. Gordon on the influential edition of Sir Gawain and the Green Knight, published in 1925. Tolkien also began developing the imaginative mythology that would later become associated with Middle-earth during these years.

Leeds is sometimes overlooked because Tolkien is most strongly associated with Oxford, where he held several important posts for decades. The question concerns the earlier university appointment, not the institution where most of his academic career took place.