Brook is one of the few Straw Hat Pirates whose origin is unknown, but his comment about Gol D. Roger might have given some insight into it.

This pirate crew is no longer active ... He eventually became a Yonko and set up his base in the land of Wano. Gol D. Roger ...

As of chapter #1109 of the One Piece manga, the previous Pirate King Gol D. Roger has yet to be known ... Kaido and Big Mom elevated Luffy and his crew to new heights of notoriety.