Tetrarch

Tetrarch, literally ruler of a fourth part of a province, was a title used in the Roman imperial system for subordinate regional rulers below the rank of king. In the New Testament it denotes any such client ruler of a territorial division (Matt. 14:1; Luke 3:1). Herod Antipas, who governed Galilee and Perea, and his brother Philip, who ruled the northeastern regions, were both tetrarchs under Roman authority following the division of Herod the Great's kingdom at his death in 4 BC.

The title carried real administrative and military power despite its lesser prestige. Herod Antipas, the tetrarch most prominent in the Gospels, is responsible for the execution of John the Baptist (Matt. 14:1-12) and plays a brief role in the trial of Jesus (Luke 23:7-12). The NT writers use the term loosely to mean any subordinate regional governor, not strictly one who rules a quarter-share.