J.R.R. Tolkien was an Oxford don and the author of 'The Lord of the Rings'. While working at a garden centre, Fitz Kreiner had a conversation with a woman who incorrectly named him as R. J. Tolkien. Fitz convinced her that the character of Frodo had been named after a woman whom Tolkien had a relationship with. (EDA: The Taint)
He briefly met Amy and the Doctor during a readthrough of The Professor, the Queen and the Bookshop by C. S. Lewis. Although he's never called by his full name, he's refered to as John and Amy says he loves "made-up languages". (DWM: The Professor, the Queen and the Bookshop)