Haoshoku Haki is a rare form of Haki that cannot be attained through training. Only one in several million people have this ability. This type of Haki allows the user to exert their willpower over others. It is said that whoever possesses this type of Haki has the qualities of a king.
Before the Wano arc, there were 9 known Conqueror's Haki users in One Piece. They included, Shanks
Kozuki Oden
Kozuki Oden was the daimyo of Kuri in Wano Country, the son of the former Shogun of Wano Country Kozuki Sukiyaki, the husband of Kozuki Toki, and the father of Kozuki Momonosuke and Kozuki Hiyori. He was the patriarch of the Kozuki Family 20 years ago until he was executed by Kurozumi Orochi. He was also a member of the Roger Pirates
.
In the chapter 924, Shutenmaru revealed that Kozuki Oden could also use the Conqueror's Haki.
Eustass Kid
Eustass "Captain" Kid
is a notorious pirate from South Blue and the captain of the Kid Pirates. He is one of twelve pirates who are referred to as the "Worst Generation" (formerly known as the "Eleven Supernovas"). Sometime during the timeskip, his bounty was raised from Beli 315,000,000 to Beli 470,000,000.
When Luffy used his Conqueror's Haki on Kaido's men, Kaido reacted by saying that, “so you too can use Conqueror’s Haki just like that other brat Kid”. He was, without a doubt, referring to Eustass Kid
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