The first name of J.R.R. Tolkien was John.
He was born John Ronald Reuel Tolkien, and the initials in his familiar author name represent John, Ronald, and Reuel. He was generally known as Ronald to family and friends rather than by his first name.
The name Reuel came from his family history and was also used as a second middle name. Tolkien's initials became so closely associated with him that many readers know the author primarily as J.R.R. Tolkien rather than by his full given name.
Tolkien's naming conventions are sometimes mixed up with those of his fictional characters. “John” refers to the author himself; it is not the name of a major character in The Hobbit or The Lord of the Rings.