NOTES for Mar 6:14-29
The figure of Herod the Tetrarch, mentioned in the Gospel, would not have appeared sympathetic either to historians or to his contemporaries. He was a petty, cruel, and suspicious tyrant with fairly pronounced sadistic tendencies, a typical representative of a degenerating dynasty. In spite of all this, he retained the formal status of a Roman ally, which he had inherited from his father. For this reason Rome, despite numerous complaints from local residents and reports from the procurators of Judea, could not fully deprive him of power, leaving him Galilee, for which the Roman authorities apparently felt less concern than for Judea.
All this did not prevent Herod from having his own peculiar notions of what he considered and called honor. He was boastful, but once he had sworn an oath in the presence of witnesses, he considered it humiliating not to keep it. Herodias took advantage of this. Judging by the Gospel account, she hated John far more than Herod himself did. Herod was content for John to be silent, or at least for his accusations not to be voiced publicly. Herodias wanted nothing less than to get rid of the prophet, to have him executed. She knew her husband well: the trick with her daughter's dance worked exactly as intended. Lust and boasting can be an utterly deadly combination, and Herod reluctantly does what he had not intended to do.
He was, however, if not religious, then at least superstitious. When he heard about Jesus, he decided that Heaven was punishing him for the murder of a man of God. Herod lived in constant fear and among many fears, so it is no wonder that he became superstitious to the point of absurdity. When a personality falls apart, even the most absurd and impossible things can appear completely real. So it was with Herod: he hated and feared John while John was alive, while at the same time involuntarily respecting him; and after executing the prophet, he began to fear his shadow.