Who is the king of the Nine Hells?

Asmodeus, the King of the Nine Hells and Lord of the Ninth, is at the very least an archdevil, but he may possess the power of a true deity. He resides in Malsheem, located on the lowest layer of Baator, Nessus.

https://dungeonsdragons.fandom.com/wiki/Lords_of_the_Nine_Hells#:~:text=Asmodeus%2C%20the%20King%20of%20the,lowest%20layer%20of%20Baator%2C%20Nessus.