Kaido

"Dammit! Hurry up, Joker! Make preparations for the final battle! I don't care if this boring world is destroyed! Let's start the greatest war the world has ever seen!"

- Kaido

Kaido (カイドウ Kaidō) is the captain of the Hundred Beasts Pirates and one of the Four Emperors in One Piece. He is the one who killed Gekko Moriah's old crew. He also tried to attack Whitebeard but was stopped by Shanks. He is also considered to be the strongest creature in the world due to having an army of Beasts, and he himself is a beast. He hires Donquixote Doflamingo to make his army.

Personality
Not much is known about Kaido's personality but it is implied by Trafalgar Law that he has a temper. He would even kill Doflamingo if something happened to the SMILE factory. He seems to enjoy suicide attempts as a hobby because of his seemingly indestructible body. It is also mentioned that Kaido is not up for negotiations. He is also very arrogant and prideful in himself seeing Doflamingo and the Supernovas as weaklings. When he is enraged, he would also take his rage out on his subordinates by attacking them.

Abilities
As a Yonko, Kaido is an extremely powerful individual. He is much stronger than Doflamingo, the latter who is incredibly strong by himself. He is even strong enough to fight Whitebeard (another powerful Yonko). Despite Kaido's menacing capabilities, not much is known about his actual powers.

Physical Prowess
Kaido is considered to be the strongest "creature" in the world. He is said to have survived countless situations where he would have been killed or executed. He has survived many types of torture and even execution. His body is strong enough to even shatter spears that would stab him. He attempted to commit suicide dozens of times but would always survive every time (even to the point of being a hobby). He is stated to be a being that is near immortal and simply cannot be killed. For instance, he fell from Ballon Terminal (a sky island about 10,000 meters above the ground) to the island where Eustass Kid's alliance was at and survived it with no scratches but just a headache.

Past
At some point, Kaido met Doflamingo and they decided that Doflamingo should supply artificial devil fruits to enhance Kaido's army. And at another point, Kaido slaughtered Gekko Moriah's comrades in the New World.

Summit War Saga
Before the Marineford War, Kaido attacked Whitebeard but Shanks stopped the fight.

Time Skip
At some point after the Marineford War, Kaido and the shogun of Wano Kuni were responsible for the death of Oden. Kaido wanted to know an important information that Oden knew but the latter refused to tell him.

Pirate Alliance Saga
Luffy and Law decided to create an alliance so that they can take down one of the Yonko, Kaido. With the SAD factory on Punk-Hazard destroyed, the Straw-Hats and Law now want to destroy Kaido's SMILE factory in Dressrosa so that it can lower Kaido's army power.

After learning about Doflamingo's defeat and the destruction of the SMILE factory by the Straw Hat and Heart pirates alliance, his men tries to informs him about the news. Kaido, however, appeared on the Sky Island called Ballon Terminal. He attempted to commit suicide by free falling at a height of 10,000 meters to hit the ground below. He landed at the base of Eustass Kid and survived the fall complaining of a headache. He came out the hole and began speaking about Joker and his desire to make him prepare for a massive war.

Yonko Saga
Kaido appeared on an island with his subordinates. He was seen drinking sake after hearing about Doflamingo's defeat at the hands of Luffy and Law. He was sad at first that he would not be able to achieve his goals of getting a devil fruit only crew. His depressive mood turn to wrath when he saw the wanted posters of Luffy and Law and decided to attack his crew mates with a giant mace out of spite. Kaido said that their decision to take down Doflamingo have now caught his attention and that he will be going after them. He began insulting Kid who happened to have been defeated in their confrontation before. Kaido stated that the Supernova are simply playing a pirates game.

Trivia

 * Like Big Mom, Kaido's appearance changed from the time he was mentioned until he made an appearance. This was possibly because it was an earlier design.
 * Kaido is the last Yonko to make an actual appearance in the series.
 * Kaido was first mentioned in Chapter 432 by Garp in his conversation about the Yonko. He makes an actual appearance in Chapter 795. This makes it 363 chapters that Kaido was mentioned before his actual debut.
 * Many fans believe that Kaido could be a Mythical Zoan devil fruit user.
 * Kaido's name means temple or church.