The “R” in J.R.R. Tolkien’s name stands for Reuel.
Tolkien’s full name was John Ronald Reuel Tolkien. He was born John Ronald Tolkien, but Reuel was added as a middle name after his father’s death. The name had family associations and was also the name of a biblical figure, the father-in-law of Moses in the King James Bible.
Tolkien is widely known by his initials because “J.R.R. Tolkien” became the form used on his books and scholarly publications. The repeated initials also make his name distinctive, while the full name appears in biographical and archival records.
Reuel is sometimes mistaken for a second given name beginning with a different R, particularly because Tolkien’s first two given names are more familiar to readers. The correct full sequence is John, Ronald, Reuel, Tolkien.