@Fleet-Admiral:
I have theory about Doc Q.
Somehow this guy is able to create diseases which effect to himself too (but still doensn't kill him?). Whole countries might died because of his work. This way he would perferct opposite to Chopper, who tries cure people as much as he can.
From the time's of plague, dead and diseases has been represented by grim reaper, which Doc Q clearly is.
Good guess. I think you are right. He surely looks like Death as one of the Horsemen of the Apocalypse.
http://www.albrecht-durer.org/72527/The-Four-Horsemen-Of-The-Apocalypse-large.jpg