One of my favorite things about One Piece is how the meaning of the letter D in Monkey D Luffy has slowly been built up as a big mystery, to the point that at the halfway point of the story I was genuinely like "holy SHIT" to find out that Gold Roger was actually Gol D Roger.
...and despite finding out more about what it means, symbolically, over the course of the series, we still don't know what it stands for.
(though at this point I'm like 90% sure it stands for )
