The Four Heavenly Kings refer to the four gods from Buddhist faith. Shitennō is also used to refer to a group of four leaders in a given field, i.e "The Big Four" or "Quadrumvirate".
Usage
See Special:Whatlinkshere/Etymology:Four Heavenly Kings for a list of articles using this term.
This is an etymology page: a page detailing the origins of terminology used in the series in regards to real world culture and history.