Appointed by his father, Antipater at the age of 25. Antiquity, 14.9.2 (see note that says 25, text says 15).
Antipater gains Roman favor by sending them money - J. Caesar Antiquity 14.9.3.
Herod gains a reputation for acting as a "violent and bold man, and very desirous of acting tyrannically" Antiquity 14.9.3.
Herod kills Hezekiah, a murderous bandit. Herod is then charged by the Jewish sanhedrin for murder because a man can only be killed if condemned by the sanhedrin. Herod refused to stand trial before the sanhedrin and, instead, gained (with money) an army from Sextus Caesar (gov. of Syria and relative of J. Caesar). Herod took the army to Jerusalem to take the city by force and kill the sanhedrin members, but was stopped by his dad and brother. Antiquity 14.9.3-5.