Bar the obvious usual suspects, Luffy-Zoro and Roger-Rayleigh (I also like Kid-Killer a lot) there even is a better duo than these two?
Kaido and King have an incredible bond, they really are such a great duo of Captain and Right Hand Man. They share a gargantuan amount of parallels that make them unique in the Beasts Pirates.
Oda made that Kaido’s strongest move and King’s strongest move are a blatant reference one to the other. The visual similarity speaks for itself. They both have the same giant avatar of a magma shaped in the form of a dragon, just Kaido has an even greater scale and power than King.
Kaido, the Beasts Pirates captain, was defeated by Luffy, the Straw Hats captain and the future Pirate King. King, Kaido’s right hand man, was defeated by Zoro, Luffy’s right hand man and the future World’s Strongest Swordsman.
Being Zoro a right hand man who is very close in strength to his captain, Zoro also fought against Kaido, gaining crazy feats and using his strength to protect Luffy, saving his captain’s life many times. Zoro’s attacks even threatened Kaido’s life, and managed to wound the Yonko to the point of inflicting him a scar.
Later, to defeat Kaido, Luffy will have to prove himself as a “King”, unlocking Advanced Conqueror Haki. Later, to defeat King, Zoro will have to prove himself as a “King”, unlocking Advanced Conqueror Haki.
Advanced Conqueror’s Haki, the power of the top tiers, the power that “only a handful of the very strongest can” was needed for both Kaido and King.
When Kaido was being defeated by Luffy, he thought of King. When King was being defeated by Zoro, he thought of Kaido.
Kaido is known for his toughness as a dragon, King is so tough that, as a dinousaur who wields the power of the Lunarians, he is tougher than even Kaido. His defense is just exceptional, even stronger than the one of Kaido’s dragon scales.
Proof: Zoro’s Tatsumaki. Oda creates a clear comparison for the readers to understand, makes Zoro use the same move, with completely different results, and puts the statement that King is something superior, in this field, to both dragons and dinosaurs.
Oh, let’s remember that King is officially stated and confirmed to be the the leader of the All Stars, and the undesputable second strongest after Kaido.
Alber was literally chosen by Kaido as his right hand man just because of Kaido being impressed by his immense strength, and granted the name of King (King > Queen > Jack) because of that superior strength.
I actually have really liked Kaido and Kings dynamics from the flashbacks we’ve got.