In the chapter Suicide on the page where Kaido makes his debut appearence. He said "THat old whitebeard did a number on me. He's immortal? Why would he say that when he fell 10,000 meters and didn't have a scratch on him? Unless whitebeard was the one that made him immortal? I believe it was OnePieceHQ on youtube that theorized That Kaido is the former first mate of whitebeard and he left because Whitebeard had no ambitions or desires to conquer anything. As his former first mate whitebeard thought of Kaido as his son. Why I say this? Because throughout Kaido's life he has experienced failure many times and became depressed. Whitebeard having care for "his son" went to the lengths of making kaido unkillable. Then Kaido set off on his own to do as he pleases. "That old whitebeard did a number on me" could mean not physically. It could explain why he attempted to attack whitebeard at marineford to get revenge.Having him being suicidal and being angry that he can't kill himself. If you don't agree. What do you think Whitebeard did to him?
[video]https://youtu.be/fOgJvvIIK5Q[/video]
[video]https://youtu.be/fOgJvvIIK5Q[/video]