The Yonkou (Four Pirate Emperors) are the four leaders of pirates in the New World. They are Red-Haired Shanks, Whitebeard (Shirohige), Kaidou and a currently unnamed one. For more information visit http://onepiece.wikia.com/wiki/Yonkou
The Yonkou are the four strongest pirates in the New World who pretty much do as they please. They are Whitebeard, Shanks, Kaidou, and another pirate known only as "Big mom"