In the world of One Piece, Kaido is famously known as the “strongest creature in the world”. Throughout the past, hundreds, if not thousands of times, Kaido has fallen into the depths of despair, yet he has never truly been “defeated” in the conventional sense.
Recently, creator Eiichiro Oda gave us a glimpse suggesting that Kaido might not be as invincible as we once thought. Before Luffy’s victory in the battle against Kaido in Wano, Oda hinted at other individuals who managed to overpower Kaido at different points in time.

Kaido in His Early Days
As a child, Kaido experienced a rather unfortunate upbringing in the Vodka Kingdom. Witnessing extreme poverty, deprivation, and continuous warfare in his homeland, Kaido understood that to have a good meal, one must fight; if one desired a full stomach, they had to go to war.
At a certain point, Kaido stated: “The value of a person can only be measured on the battlefield! Where everything is at stake!” Hence, it is not surprising that Kaido sought to harness power and control over others.

After encountering Rocks D. Xebec and being introduced to the Rocks Pirates, Kaido transformed into a formidable figure within the crew and earned respect from fellow crew members, marking the beginning of his notorious reputation.
Despite being just a recruit, Kaido was one of the strongest members of the crew. In chapter 1096 of the One Piece manga, it is revealed that Kaido was given a different title that reflected his past before he achieved his current legendary status. This only serves to highlight the many failures that contributed to the image of Kaido we know today.
Kaido during the God Valley Incident and the Shadow of Roger
Delving into the events surrounding Kaido’s early career with the Rocks Pirates, particularly during the infamous God Valley incident when the Rocks crew disbanded, we see Big Mom bestowing upon Kaido the Zoan-type Devil Fruit, the Uo Uo no Mi. Following this, Kaido chose his own path, forming the Beast Pirates and rising to become one of the most powerful figures in the world.

However, chapter 1096 also exposed Kaido’s connection with Gol D. Roger, indicating that Roger had once bested Kaido at some point before the God Valley incident. This revelation suggests that Roger had a significant impact on Kaido’s life during their earlier encounters.
Many years before the God Valley incident, specifically 39 years ago, a major battle occurred between the Rocks Pirates and the Roger Pirates. At that time, Kaido was just a rookie. It is likely that the aspiring pirate Kaido had a direct clash with Roger.
Nevertheless, at that moment, Kaido was merely a fledgling pirate who had not yet attained the title of “the strongest creature in the world” that we recognize today. Therefore, it is not surprising that he could be bested by Roger in a fair fight.
The shadow of Kaido’s strength made him despise defeat, which leads many to speculate about the emotional weight he felt after losing to Roger. At that time, Kaido was still young, unaware of the pinnacle of his strength, while Roger was an experienced and formidable captain. Roger not only had more experience but also superior Haki mastery. Hence, it is reasonable that Kaido’s defeat and subsequent hatred towards Roger stemmed from this experience.
In summary, the battle that took place 39 years ago was not merely a typical skirmish. It was a clash of ambitions, a confrontation of evils, and a quest for supremacy. Each character had their reasons, motivations, and personal demons to confront during that fateful encounter.