However, there are situations where you might hyphenate a similar phrase:
* If it's used as an adjective: "He was a priest-king figure in the ancient civilization."
* If it's a compound noun that's unclear without a hyphen: "The priest-king's robes were magnificent." This clarifies that "priest-king" is a single entity.
In general, though, it's best to stick with "priest king" as two separate words unless the context requires a hyphen.