Herod II (ca. 27 BC – 33/34 AD) was the son of Herod the Great and Mariamne II, the daughter of Simon Boethus the High Priest (Mark 6:17). For a brief period he was his father's heir. Some writers call him Herod Philip I (not to be confused with Philip the Tetrarch, whom some writers call Herod Philip II).
Herod was the first husband of Herodias, and because the Gospel of Mark states that Herodias was married to Philip, some scholars have argued that his name was actually Herod Philip. Many scholars dispute this, however, and believe the Gospel writer was in error, a suggestion supported by the fact that the later Gospel of Luke drops the name Philip. Because he was the grandson of the high priest Simon Boethus he is sometimes described as Herod Boethus, but there is no evidence he was actually called this.
Herod the Great's execution of his two sons born by his Hasmonean wife Mariamne, Alexander and Aristobulus IV in 7 BC, left the latter's daughter Herodias orphaned and a minor. Herod engaged her to Herod II, her half-uncle, and her connection to the Hasmonean bloodline supported her new husband's right to succeed his father.
As Josephus reports in Jewish Antiquities (Book XVIII, Chapter 5, 4):
Herodias, [...], was married to Herod, the son of Herod the Great by Mariamne, the daughter of Simon the High Priest. [Herod II and Herodias] had a daughter, Salome...
This led to opposition to the marriage from Antipater II, Herod the Great's eldest son, and so Herod demoted Herod II to second in line to the succession. Antipater's execution in 4 BC for plotting to poison his father seemed to leave Herod II, now the eldest surviving son of Herod the Great, as first in line, but his mother's knowledge of the poison plot, and failure to stop it, led to his being dropped from this position in Herod I's will just days before he died.