Mweheheee, Demon King Belphegor!
I almost can’t wait until I get to drawing his reference someday in the future.
Anyway, for now, have a bust of a Demon King.
He has ruled Hell for a little over 1000 years after he killed his predecessor Set. Pretty much describes how a new Demon King is “chosen” to rule - they kill off the ruling King and take his/her place.
Yes, even the females call themselves Demon King.