User blog comment:Monkey.D.Me/Theory on Void Century/@comment-182.52.2.221-20140624083231

then the survival from Ancient Kingdom decided to add the "D" to their name in order to tribute to their Leader and longer their lineage also, they will able to identify if person have their blood, by the initial "D"

Portgas XXX Marshall XXX Monkey XXX Gold D. XXX (leader) Jaguar XXX