Herod is certainly a bad guy in this story. He was a paranoid king who had members of his own family killed including a wife and 3 sons because he thought they were out to get him. He did have some accomplishments, yet he also was seen as very ruthless and cruel.
Herod's fear of Jesus comes because he is not a legitimate King. He had kingship that was given by Rome, not God. We also know that he was not
the legitimate heir to David's throne. He was constantly feeling threatened and paranoid. King Herod requested that the Wise Men return with a location so he could worship the newborn king. Herod only worshipped himself though. No king on this earth is a match or a threat for the King of Kings.