10 - Shakky
Shakky's strength is not fully known, but one may assume that she has at the least some fighting powers as a former pirate as she is always rivaled by Garp the Hero.
9 - Bartholomew Kuma
After the war in marinefold, there are no clues to what happen to Kuma, whether he is alive or dead cyborg only dragon knows.
8 - The 7th Shichibukai (Warlords)
Up to this day no one knows who is the seven Shichibukai, he might be the most powerful among the all Shichibukai.
7 - Dracule "Hawk Eyes" Mihawk
Still nobody know why Mihawk chose to live alone and how he became the world's greatest swords man.
6 - Joyboy
Joyboy is mentioned by Robin after reading a poneglyph on fishman island. Still unknown why Joyboy is apologizing to??
5 - Roger Pirates
Only Rayleigh, Crocus, Shanks and Buggy are well known Roger Pirates, the rest are still unknown or where they might be.
4 - Dr. Vegapunk
He is the one who convert Kuma into a Cyborg. Dr. Vegapunk's whereabouts remains a mystery. It is not known which side he is, (Goverment or the revolutionaries?).
3 - Klabautermann
Klabautermann is a spirit fairy of Going Merry, is also the one who made temporary fix for damages on Going Merry, whether the Strawhat pirates will see him again remains a mystery.
2 - Monkey D. Dragon
Aside from being Luffy's father and the most wanted criminal in One Piece, not much is known about Dragon, nobody knows what kind of Devil Fruit user is he, nor his abilities and powers.
1 - Gol D. Roger
The Pirate King Gol D. Roger power and abilities are unknown, wether he is a Devil Fruit user or not. Some theorist said that he is the former Gomu-Gomu no Mi but this is not yet confirmed, all we know is he is the "original owner" of "Strawhat".