Albert Barnes on Matthew 14:1

Herod the tetrarch. See also Mk 6:14-16; Lk 9:7-9. This was a son of Herod the Great. Herod the Great died probably in the first year after the birth of Christ, and left his kingdom to his three sons, of whom this Herod Antipas was one. He ruled over Galilee and Perea. Mt 2:16. The title tetrarch literally denotes one who rules over a fourth part of any country. In a remote signification, it means one who rules over a third, or even a half of a nation.

Heard of the fame of Jesus. Jesus had then been a considerable time: engaged in the work of the ministry, and it may seem remarkable that he had not before heard of him. Herod might have, however, been absent on some expedition to a remote part of the country. It is to be remembered, also, that he was a man of much dissoluteness of morals; and that he paid little attention to the affairs of the people. He might have heard of Jesus before, but it had not arrested his attention. He did not think it a matter worthy of much regard.

(v) "Herod" Mk 6:14, Lk 9:7