The people of the D have always been massive mysteries in the One Piece world. Monkey D. Luffy was introduced to the fans right at the beginning of the story, and it was here that fans first started questioning the meaning of the D. As One Piece continued, the meaning of the D got even more intriguing, as several other characters with this initial in their name started appearing, and at the same time, characters who are intrigued by the true history of the world started digging deep into the meaning of the letter as well.