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John the Baptist was a man in the Bible who preached of the coming of Jesus. He was the man to baptize Jesus in the River Jordan, as recorded in the book of Matthew. John the Baptist was the cousin of Jesus. His mother was Elizabeth.
The synoptic gospels (Matthew, Mark and Luke) say
that John the Baptist was a preacher who baptised Jesus just before
Jesus began his ministry.
Luke's Gospel also says that John was related to Jesus, his mother being Elizabeth, a cousin of Mary the mother of Jesus. Nevertheless, when John was in prison he sent messengers to Jesus, asking of him whether he was the one he had promised would come, although it seems hardly likely that he would need to ask this of Jesus if they were relatives. John's Gospel says that John did not even know Jesus until he saw the dove descend upon him. There seems good reason to doubt whether John and Jesus were really related, although they would seem to have been contemporaries.
According to the synoptic gospels, John the Baptist was executed at a party that took place in Galilee around 29 CE, shortly after the beginning of the mission of Jesus. The Jewish historian Josephus said that Herod Antipas had the Baptist killed far away from Galilee and in quite different circumstances, because he disapproved of Antipas' marriage to his own brother's wife, who divorced her husband in order to marry Herod Antipas. The wedding took place in 34 CE and the execution of John would have been in 35 or 36 CE. The relevant text from Book 18 of Antiquities of the Jews:
"Now many people came in crowds to him, for they were greatly moved by his words. Herod, who feared that the great influence John had over the masses might put them into his power and enable him to raise a rebellion (for they seemed ready to do anything he should advise), thought it best to put him to death. In this way, he might prevent any mischief John might cause, and not bring himself into difficulties by sparing a man who might make him repent of it when it would be too late. Accordingly John was sent as a prisoner, out of Herod's suspicious temper, to Macherus, the castle I already mentioned, and was put to death."
King Aretas of the Nabateans attacked Herod Antipas in 36 CE because of the insult to his daughter whom Antipas had divorced in order to marry his brother's wife, leading the Jews to believe that this was God's way of punishing Antipas for the death of John the Baptist. This must therefore have been shortly after the death of John.
Members of the Mandaean religion say that John the Baptist was the founder of their faith, and that his name was stolen by the early Christians. Another view, based on scant extra-biblical information about John, is that he might have been the leader of an early Gnostic sect.