The Lesser Key of Solomon
He is the king of the west according to some translations of The Lesser Key of Solomon, and king of the south according to Pseudomonarchia Daemonum. The other three demon-kings of the cardinal directions are Amaymon, Ziminiar, and Gaap (although some translations of "The Lesser Key of Solomon" consider Belial, Beleth, Asmodai, and Gaap to be the kings of different cardinal directions, not specifying the cardinal direction that they rule over).