shichibukai

The Seven Warlords of the Sea (王下七武海, Ōka Shichibukai) are a group of seven pirates allied with the World Government in One Piece. The roster has fluctuated as the story has progressed, but there's never more than seven at the same time.

However as a result of both Sir Crocodile enacting Operation Utopia in Arabasta and Donquixote Doflamingo becoming the tyrannical ruler of Dressrosa, the system was eventually disbanded.

Members (as of the disbandment):

Bartholomew Kuma
Boa Hancock
Buggy the clown
Dracule Mihawk
Edward Weevil

Former Members:

Crocodile
Jinbe
Marshall D. Teach
Gecko Moria
Trafalgar Law
Donquixote Doflamingo

Candidates:

There have been other pirates who have been selected to become Shichibukai but did not receive membership for one reason or another.
Portgas D. Ace