Who was 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).

Tetrarch first appears in Matthew 14:1. In this repository’s biblical text, this figure is associated with 5 verse mentions across 3 books, most notably Luke, Matthew, Acts.