We also learn that he is the one managing the crew.
He always looked like that guy to me.
- King summoned the Tobiroppo (even tho using Kaido's name)
- King took the Den Den Mushi and gave instructions when the raid officially started
- King kept contact with the Marys to get updates from the battlefield and deploying counter-instructions
Also, a point that shouldn't be overlooked, in a crew of beasts and brutes he looks like the most
cerebral to me...