At that time Herod the tetrarch heard the reports about Jesus… Matthew 14:1

In the fifteenth year of the reign of Tiberius Caesar—when Pontius Pilate was governor of Judea, Herod tetrarch of Galilee, his brother Philip tetrarch of Iturea and Traconitis, and Lysanias tetrarch of Abilene… Luke 3:1

            A tetrarch is a governor of a part of a country or region.  He could be one of three or four other governors, sub-ruling under a greater ruler of the whole part.  Tiberius Caesar was the big boss (or President) and Pontius Pilate was like the governor of a state.  Herod the Great was a tetrarch, as was his son, Herod Antipas, over the area of Galilee.  Philip and Lysanias were also tetrarchs mentioned in Luke.  They were more like a mayor of a city or county commissioner.