User blog comment:Gametroller Prime/Four Great Powers?/@comment-34981281-20160218045430/@comment-71.13.82.131-20160218164028

The name themselves when they beat you down. The Yonkou is more a status for the top tier pirates of the New World, there is no reason there can't be more or less than 4 of them. From what we have seen, to be a Yonkou you need a lot of influence in the New World, such as protecting/owning territory and having a large enough following of pirates to keep that influence.