Ruler of Hell

King or Queen of Hell is a title and the highest position a demon can hold over Hell. King of Hell can control the fate of any soul that goes to Hell. The King has such a high authority that he or she may even trade any number of souls in Hell as per their wish, as seen when Crowley gave Castiel "fifty large," fifty thousand souls from the 'pit,' to make a showing in front of Raphael during the civil war in Heaven. While other demons have ruled Hell previous to them, only Crowley and Abaddon have used this title to describe themselves.

Known Kings of Hell.
Azazel (season 1 -2 )

Lilith (season 3 -4 )

Lucifer (original) (season 5 )

Crowley (season 6 -7 -8 -9 )