The Bible records the actions of two people named “Herod”, but in reality there were at least three in the Herodian Dynasty who bore that name. This dynasty started with Herod the Great, aka Herod I, of whom Wikipedia says:
Herod (Hebrew: הוֹרְדוֹס, Hordos, Greek: Ἡρῴδης, Hērōidēs), also known as Herod I or Herod the Great (born 73 or 74 BCE, died 4 BCE in Jericho, according to one writer, 1 BCE), was a client king of Israel. He was described as "a madman who murdered his own family and a great many rabbis." He is also known for his colossal building projects in Jerusalem and elsewhere, including the rebuilding of the Second Temple in Jerusalem (sometimes referred to as Herod’s Temple) and the construction of the port at Caesarea Maritima.
Herod was the son of Antipater, an Idumean (of Edomite descent), and Cyprus, the daughter of an Arabian sheik. Antipas came to power by backing Hyrcanus, one of two princes who fought over Jerusalem. Antipas used his position to get Herod appointed as governer of Galilee.
Antipater would have been called an “Idumean Jew”, as he was a convert to Judaism as were some others of Edomite descent. However, the Jews looked down upon the Idumeans, and so this became a sore spot when Herod petitioned Mark Antony to award him the title of Tetrarch (“ruler of a quarter”) of Galilee. Worse, there is the Jewish belief that if your mother is not Jewish, then you are not really a Jew. The appointment of Herod as tetrarch rubbed a lot of the Jewish populace the wrong way.
There are two things in the NT that stand out about Herod the Great. One is building programs he engaged in, particularly that of the Temple. These building projects were an obvious attempt to win the support of the Jewish population. However, Herod tended to favor Greek architecture, and so it actually distanced him from some of those he sought support.
However, when it came to authority, he was a Roman ruler. An golden eagle perched on top of the gate of the new Temple, a symbol of Roman authority. His taxes ran quite high for that period in history, up to 20% annually, and revolts weren’t unheard of. Herod resorted to informants and violence on more than one occasion.
Some attribute the destruction of a monastery at Qumran of the Essene sect in 8 BCE to Herod, burning students and teachers alive.
You wonder about what sort of mind would kill infants two years and under, which is the other thing that stands out in the NT about Herod. There is no corroborating historical evidence of that event, but it may just be that it was lost in the long list of brutality he inflicted upon the region.
Herod had ten marriages. He had many sons. At least three were executed (see Wikipedia chart at bottom of cited article) because Herod did not trust them. Perhaps it was a self-fulfilling prophecy, but Antipater, Herod’s oldest son, was convicted of trying to poison him in 5 BCE. Archelaus was eventually named successor as king in his will, but after his death this was successfully fought and Herod Antipater became the vassal king instead.
According to an article by Jona Lendering, “King Herod the Great”, on Livius:
A horrible disease (probably a cancer-like affection called Fournier’s gangrene) made acute the problem of Herod’s succession, and the result was factional strife in his family. Shortly before his death, Herod decided against his sons Aristobulus and Antipater, who were executed in 7 and 4 BCE, causing the emperor Augustus to joke that it was preferable to be Herod’s pig (hus) than his son (huios) – a very insulting remark to any Jew.