Herod was not born a Jew. His mother was the daughter of an Arabian sheik and his father, Antipater, was an Edomite-- a pagan people living in what is now Jordan. Antipater was a gifted opportunist who backed the right Hasmonian prince in a succession struggle and managed to marry a Hasmonian princess and secure an appointment at court. Next, he displayed excellent political judgment in backing Julius Caesar in the civil war against Pompey. For backing Caesar, Antipater obtained the appointment of his twenty-five-year-old son Herod as governor of Galilee. Soon after taking office Herod suppressed an uprising led by Hezekiah (or Ezekias), and put him and a large number of his followers to death. Taking "the law into his own hands got him in grave trouble with the Jewish Council in Jerusalem," a conflict with religious Jews that was to continue throughout his life.
After Caesar was murdered, his assassins Brutus and Cassius took control of the East and demanded funding from the local rulers. Herod complied but eventually fled to Rome where he somehow gained the favor of Mark Antony and the Second Triumvirate, and they caused the Senate to elect him "King of the Jews." With this backing, in 37BCE Herod gained the throne of Judea. To help secure his claim to the throne, he banished his wife and son and then married his teenage niece.
Herod claimed to be a Jew, but many Jews did not accept him as such. In an effort to gain support from the more traditional Jews, Herod undertook a massive rebuilding of the Temple in Jerusalem on a far more magnificent scale. Later he greatly compromised this achievement by placing a huge golden eagle over the main entrance to the Temple. This was hotly condemned by leading Pharisees as an idolatrous Roman symbol, and some young zealots smashed it during the night, for which they were arrested and burned to death by order of Herod.
As king, Herod was empowered to appoint the high priest. Being cautious about possible rivals, as his first selection he appointed "an obscure Jew from Babylonia." This infuriated his mother-in-law and eventually Herod withdrew the appointment and gave the job to his mother-in-law's seventeen-year-old son Aristobulus. Soon after, Herod arranged a bathing party at Jericho, at which he had Aristobulus drowned. Subsequently, in an effort to overcome their angry opposition, Herod began to appoint Sadducees (the hereditary priestly class) to the high priesthood, each serving a short term and retaining his privileges after leaving office. This helped in building a base of influential religious supporters. But they were of little help in shielding him from growing religious antagonism, some of it based on his dreadful family life.
During his reign, Herod ran through ten wives and not only disinherited his sons from previous marriages, but had at least three of them murdered. Late in his reign he became very alarmed at the rapidly growing outbreak of messianic hopes and prophecies, and anyone he suspected of being the Messiah he had put to death. When he became suspicious that his current wife was involved with a group expecting the Messiah, he had her killed too. Matthew 2:16 claims that, hoping to eliminate Jesus, Herod ordered the death of all the children under the age of two in Bethlehem. Whether or not this actually happened, it was utterly in character.
~The Triumph of Christianity, Rodney Stark, 2011