Mukarrib (Arabic: مكرب) is a title variously defined as "priest-kings" or "federators"; the mukarribs may have been the first rulers of the early South Arabian states. Sometime in the fourth century BCE, the title was replaced by mlk, typically translated as "king".
Scholarly interpretations
Stuart Munro-Hay writes that the title of mukarrib "indicates something like 'federator', and in southern Arabia was assumed by the ruler who currently held the primacy over a group of tribes linked by a covenant."
Joy McCorriston took a slightly different viewpoint:
[I]t is clear that early (800-400 bc) political authority resided with one leader - a mlk, or king of his own ethnic tribe ...appointed as mukarrib of a council of tribal leaders. The mukarrib issued edicts that carried out decisions by the council and presided over building projects, ritual hunts, and sacrifices. Some of the most famous inscriptions record the military conquests of mukarribs, who were evidently quite successful in confederating tribal groups through the rites of pilgrimage (at Jabal al-Lawdh, for example) and then using such social cohesion to conscript military forces.