Some quick research renders this:
William Branham was a protestant fundamentalist who has been credited with various prophesies and visions, supposedly from God. He claimed to preach the true Christian faith, and his followers today consider all Branham’s teachings to be inspired by God and to be infallible interpretations of Holy Scripture.
He rejected Trinitarianism (though he seems to have accepted it early on), and accused Catholicism of teaching the existance of three Gods in the Nicene Creed. God the Father, Son and Holy Spirit are not three distinct persons in Branham’s teachings, but three incarnations God. He also taught that Eve had sexual intercourse with the Serpent in the Garden of Eden, and therefore humans are descended from Satan.
Branham was involved in various occult practices, including astrology. He claimed that God created three sets of scripture- the Zodiac, the Great Pyramid, and the King James Bible.
He seems like just another radical protestant fundamentalist with a spiritualist flavor.