It's possible you are thinking of:
* J.R.R. Tolkien: The author of "The Lord of the Rings," which features Rohan as a kingdom. However, "J.R.R." stands for John Ronald Reuel Tolkien, not "J.R."
* Riders of Rohan: A term used to describe the Rohirrim, the horse-riding people of Rohan from Tolkien's books.
Please clarify your request with more information about who or what you are looking for.