User blog comment:Kaido King of the Beasts/Chapter 934: High Hyopes/@comment-4401815-20190222122138/@comment-50.202.177.251-20190302003407

Generally the theory before was him being a scorpion (due to the scorpion ships that helped Jack during Zou) and his har style resembling a scorpion tail.

With King turning out to be a Ancient Zoan, however, theories have shifted towards prehistoric scorpion, typically a sea scorpion. Would fit in with the other Ancient Zoan's, but make him represent sea like how Jack represents land and King represents air. And, while he can't swim, his hybrid form would still function on land and provide all the best features of the sea creature in question, before anyone complains about a sea creature for a DF.

But hopefull we find out in the next chapter.