Although he acted as governor of Judea—appointed by Rome, he was a people-pleaser at heart. Herod acted big for the guests at his birthday party. His step-daughter had danced for those in attendance. After she finished, Herod boasted he'd do anything she asked, he was so appreciative of her dancing.
Her mother, Herodias, put her up to it. She told her to ask for John the Baptist's head on a platter. This bothered Herod. He actually liked John, except when his preaching went to meddling into Herod's life.
Herod first thought Jesus was John the Baptist come back to life. When approached by the crowd, he didn't know what to do about Jesus.