Kaidou
One of the Four Emperors and captain of the Beasts Pirates, Kaidou holds the title of "the strongest creature in the world"—a reputation that's stuck around for good reason. He was actually the third Yonkou to get a name-drop in the story, first mentioned by Gekko Moriah right after Moriah had taken Luffy's shadow. We found out what Kaidou was actually about once the Straw Hats took down Moriah.
What sets Kaidou apart is the scale of his operation. His crew includes an army of roughly 500 artificial Zoan Devil Fruit users, which basically amounts to a small military force of superpowered combatants.
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