John the Baptist was a relative and precursor of Jesus who lived in the Judean desert. He baptized people in the Jordan River and preached repentance. John recognized Jesus as the Messiah and baptized him, marking the start of Jesus' public ministry. However, John criticized Herod Antipas for marrying his brother's wife, resulting in Herod beheading John at the request of Salome. John paved the way for Jesus and is considered the forerunner of the Messiah.