John was the prophet who preached the coming of Christ as the Messiah. He was related to Jesus through his mother Saint Elizabeth, cousin of the Virgin Mary.
John preached in the desert, baptising in the river Jordan those who repented their sins. Jesus came to be baptised, and was revealed as the Son of God; this was the most important act of John's life.
John criticised King Herod for taking his half-brother's wife, Herodias. Shortly after Jesus' baptism, Herod ordered John to be beheaded at the request of Salome, Herodias' daughter. Salome's dancing had so pleased Herod that he had agreed to grant her anything that she wanted. At her mother's prompting she asked for the head of John the Baptist.