Tetrarch

strictly the ruler over the fourth part of a province; but the
word denotes a ruler of a province generally (Matt. 14:1; Luke
3:1, 19; 9:7; Acts 13:1). Herod and Phasael, the sons of
Antipater, were the first tetrarchs in Israel. Herod the
tetrarch had the title of king (Matt. 14:9).