Nickname: "Rus"

Son of Herod the Great & Mariamne II.
Half-brother of Antipas.
First husband of Herodias.
Father of Salome II.

Fourth son, namesake & briefly heir apparent of Herod the Great. After Herod I executed his Hasmonean sons, Alexander & Aristobulus IV (7 BCE), he betrothed the latter's orphaned daughter (Herodias) -- who was still a minor -- to her half-uncle, Herod junior. This arranged marriage was more than temporary child custody.  For Herodias was descended directly from the dynasty of priest-kings that had ruled Jerusalem for more than a century before Herod. Since this liaison bolstered the young Herod's right of succession to the throne of Judea, the king's oldest son (Antipater III) objected to the arrangement. So, Herod confirmed the latter as his heir & relegated the young Herod to next in line.

When Antipater was executed for planning to poison his father (4 BCE), the younger Herod became his father's oldest surviving son. But, since the elder Herod had discovered that the younger's mother (Mariamne II) had known of the plot against him & done nothing to prevent it, he dropped her son from his will just days before he died.

Although Herod II survived his father's deathbed purges, he was left a private citizen while his remaining half-brothers divided his father's realm. This eventually cost him his marriage. Although he did marry Herodias & had a child by her, she left him for his younger half-brother, Antipas. After that the younger Herod slipped into anonymity.  In less than a generation even his name was forgotten by the public;  so, at least two of the gospels (Mark & Matthew) confused him with Antipas' other half-brother, Philip.* 

References: Josephus, Antiquities 17.14-19, 53,* 78;
                                                       18.109-110, 136-137.
                  _____, War 1.557,* 562,* 573, 588, 599-600.
                 Mark 6:17-18 // Matt 14:3-4.

*NB: This confusion led Wm. Whiston, convinced of the accuracy of the gospels, to append the name "Philip" to the name of the son of Mariamne II at some points in his 1895 English translation of The Works of Flavius Josephus, even though it is not found there in the original Greek text.