Jesus never called himself God and neither did his disciples.
300 years later, the Roman Empire adopted Christianity as its state religion and at the same time Jesus became God.
Bart D. Ehrman started life as a hard core, born-again, fundamentalist Christian, then he started reading the texts very carefully.
He has diploma from the Moody Bible Institute and a Ph.D from the Princeton Theological Seminary.
"For conservative Christians, Ehrman is a bit of a bogeyman, the Prof. Moriarty of biblical studies, constantly pressing an attack on their long-held beliefs about God, Jesus, and the Bible.... For secularists, the emerging generation of 'nones' (who claim no religion, even if they are not committed to atheism or agnosticism), Ehrman is a godsend."