"JRR Tolkien" refers to someone who is deeply immersed in high-fantasy lore, especially that of J.R.R. Tolkien's Middle-earth, often to the point of being seen as overly devoted or pedantic about the details.
He was called JRR Tolkien for quoting the Silmarillion during a board game.
She's such a JRR Tolkien that she maps out fictional cities for fun.
Don't be a JRR Tolkien; no one cares about the Elvish grammar here.