The first name in J.R.R. Tolkien’s full name was John.
His complete name was John Ronald Reuel Tolkien. The initials by which he became famous came from his first three names: John, Ronald, and Reuel. “Reuel” was a family name associated with Tolkien’s father’s side and was not simply a title or invented author name.
Tolkien was commonly called Ronald by relatives and friends during much of his life. His wife, Edith, also knew him as Ronald. Readers therefore sometimes assume that Ronald was his first name, but it was his middle name.
The initials J.R.R. became inseparable from his professional identity as a philologist, university teacher, poet, and author. His publications, including The Hobbit and The Lord of the Rings, appeared under the abbreviated form. His son Christopher Tolkien later became an important editor and publisher of his father’s posthumous writings.