Akagami Shanks Shanks is recognized as the master of conqueror's haki and the killer of observation haki too. He is also one of the few pirates who can use all three types of haki.
As expected, all of his powers are quite fearsome and Shanks is a true master of Haki. One such ability of his has earned him the title of the "Killer of Observation Haki."
When Luffy realized he needed to get stronger, he took two years off from his pirate adventures to train on Rusukaina. During this time, Silvers Rayleigh taught him the basics of using Haki. By the end of his training, Luffy had become proficient in all three types of Haki.
Roronoa Zoro is a member of the Straw Hat Pirates. Zoro was the first person who accepted Luffy's invitation and joined the latter on his journey to become the Pirate King. Zoro is a very powerful fighter and he possesses all three types of Haki. Zoro was able to use Conqueror's Haki unknowingly against Kaido.
Sanji's Haki Types
Sanji is an extremely skilled Haki user. During the two years he spent at Maiden Island, he trained his usage of both Armament and Observation Haki. Unlike Zoro and Luffy, Sanji wasn't taught this skill by anyone. He managed to learn all by himself and that is certainly an incredible feat.
Roger used advanced forms of conqueror's haki as he imbued his sword with conqueror's haki and clashed with Whitebeard. He also used advanced armament haki for more powerful sword attacks. Additionally, Roger possessed the observation haki, thus, making him the strongest haki user of all time in One Piece.
Monkey D. Luffy has mastered all three types of haki, including Kenbunshoku Haki (Observation Haki), Busoshoku Haki (Armament Haki), and Haoshoku Haki (Conqueror's Haki). He can even use several subforms of the hakis, which makes him one of the most powerful haki users in the One Piece world.
In fact, Nami has already demonstrated abilities similar to Haki. During the Alabasta Saga, she has shown the ability to tell even the slightest of changes in weather which, according to Vivi, is beyond human comprehension.
Roger ended up raising Shanks on his own ship like his own son. It can be assumed that Shanks is the son of none other than Saint Garling Figarland This also makes sense, given the fact that Garling Figarland doesn't appear to be all that old.
He is known for being the Killer of Observation Haki as he is able to stop people from being able to use it as seen from Kidd. He also has masterful control over the aspect of pinpointing specific individuals over far distances, as seen in Wano and Elbaf.
Conqueror's Haki is one of the rarest powers to exist in the One Piece world. Unlike the other two Haki forms, this power isn't accessible by everyone but exists within only a chosen few.
Garp possesses Haoshoku Haki, which is the rarest form of Haki for those who holds the qualities of a "King". He once remarked on how Luffy inherited it at Marineford. More than most, he has mastered it to the fullest, being able to perform feats beyond knocking out weaker-willed opponents.
While this is shown to be a very rare gift among the world as a whole, it is noted by Don Chinjao that the New World is filled with numerous others who possess the ability to use this Haki. He explains that Luffy will most certainly encounter them and fight them for the title of Pirate King.
Those who have mastered the fourth form of Haki will be able to manipulate nature as they see fit. They can cause living organisms to grow rapidly or die rapidly (though not resurrect them), and make objects move with the force of their minds, akin to telekinesis.
The known users of Conqueror's Haki in One Piece include Monkey D. Luffy, Roronoa Zoro, and Gol D. Roger. Conqueror's Haki, also known as the Haki of the Supreme King, is the rarest form of Haki that only a few people in the world of One Piece are born with.
In the anime, some Haki users are shown surrounded by different color auras (such as red for Luffy, purple for Doflamingo or pink for Big Mom) even if they are not using Haki at that moment.
They're literally giving characters their own colours of conquerors. Kaido's is purple, Luffy's is gold, and Zoro's is green.
Armament Haki is a power that Dragon most certainly possesses. Although not everyone in the story has Armament Haki, it is impossible for someone of Dragon's stature to not be a great user of this ability.
Roger possessed immense physical strength. He could also clash evenly with Edward Newgate, the Strongest Man in the World, matching him in strength. Roger possessed immense endurance and vitality even when he was ravaged by an incurable disease.
In One Piece, the Conqueror's Haki, especially in its advanced version, is a requirement for the strongest fighters. So far, Sanji certainly lacks this rare power. Some fans speculate that he may display it sooner or later like Luffy and Zoro did.