Who demanded the head of John the Baptist?

Salome was the one who asked of King Herod the head of John the Baptist. Salome had pleased Herod by dancing before him and Herod asked her to choose a reward, even if it be have his kingdom. Salome consulted with her mother, Herodias, with whom Herod was having an affair. Angered by John's public condemnation of this adulterous affair, Herodias told Salome to ask for John's head. You can read this account in The Bible in St. Matthew 14:6-8.

Of interest, tradition records that Salome had a bad end, accidentally becoming impaled on a wedge of ice during an elaborate banquet.