After reading Chapter 907 and Chapter 908, I came to the conclusion that the D. Clan are former World Nobles. I think in the span of 800 years some Families of the World Noble or say “Gods” started to have a change in personality and, thus, started to become more “human”; notably the Donquixote family, as we could see with Homing, Mjosgard and Rosinante. Those “fallen gods” became “god’s natural enemy”, because their ideological change threatened to topple the existing world order. And as we learned from the Chapter 908, this trait seems to be inherent to the Donquixote Family whose members, as Rosewald remarks, are nuts (not normal) in his opinion. They either become a threat to the World Goverment due to their overwhelmingly good nature (Luffy, Homing etc.), or due to their extremly violent and mad behavior (Blackbeard, Donflamingo). Consequently, I would argue that the characters who share the middle initial D. are all descendant of members of the Donquixote family, and thus former World Nobles. I even think that the mysterious character “Im” is also a Donquixote, who hates everything that threatens to change the world order (like the D. Clan, or potential ancient weapons user). To further support my theory, I would like to point out that Homing as well as Rosinante smiled right before they died. I also want to include that the Name Donquixote is based on a spanish novel in which the main protagonist loses his sanity and decides to set out to revive chivalry, undo wrongs, and bring justice to the world. You see the similiarity?