The historical John, יוחנן, was a thoroughly Jewish religious preacher, who had little if any relation to Jesus and his movement. Here is the story of how John and his central rite, baptism, became part of Christianity.For more on John the Baptist, see here and links and here. For many posts on Machaerus, the reputed site of John's execution, see here and links.
The Gospel of Thomas has an enigmatic mention of John the Baptist in Logion 46:
(1) “From Adam to John the Baptist, among those born of women there is no one who surpasses John the Baptist so that his (i.e., John’s) eyes need not be downcast.”
(2) “But I have also said: Whoever among you becomes little will know the kingdom, and will surpass John.”
The Mandeans (Mandaeans), an ancient Mesopotamian Gnostic sect who still exist today, are followers of John the Baptist without involving Jesus.
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