About Kaidou
Kaidou of the Beasts, renowned as the world's "Strongest Creature", is the Governor-General of the Beasts Pirates and was formerly one of the Four Emperors who ruled over the New World. He is also the father of Yamato.
Once a child soldier in the service of the Vodka Kingdom, Kaidou escaped being drafted by the Marines and joined the legendary Rocks Pirates as an apprentice in his teenage years. A few years after the God Valley Incident, he formed his own pirate crew and built it up into a powerful military force determined to challenge the World Government and change the world. Kaidou then joined forces with Wano Country's shogun Kurozumi Orochi and occupied Onigashima as his base for nearly three decades. In the present day, Kaidou formed an unprecedented pirate alliance with fellow Emperor and former crewmate Big Mom for the purpose of taking over the world. He then betrayed Orochi to enact his New Onigashima Project for Wano. The plan never came to fruition, however, as Onigashima was raided by the Ninja-Pirate-Mink-Samurai Alliance on that very same night and Kaidou was ultimately bested by Monkey D. Luffy. Following this defeat, Kaidou lost his position among the Four Emperors.
Kaidou was first referred to by Monkey D. Garp in the Post-Enies Lobby Arc when he revealed the existence of the Four Emperors, and was then first directly mentioned by Gecko Moria in the Thriller Bark Arc. Before he debuted in person, his voice was heard in a flashback that Kouzuki Momonosuke had when first disembarking on Dressrosa.
Due to his actions, he can be considered the overarching antagonist of the Dressrosa Saga, the main antagonist of the Wano Country Arc and Saga, and a major antagonist of the second half of the series.