Okay, so my friend and I are having a discussion and he is under the impression that Jesus (the man who can be reasonably assumed to have existed) never actually claimed to be the son of god personally, and that was just written in later by Saul/Paul. Are there any non-biblical sources that speak to this issue one way or another?
Disclaimer, I did look through your archived religion posts, and while the ones on Jesus's actual existence were helpful, they did not really answer this particular question
It might be worth checking out and asking r/AcademicBible. Plenty of discussion with some really knowledgeable people.
One of the oldest (possibly THE oldest) pieces of artwork depicting Jesus of Nazareth is actually blasphemous to Christians and is dated roughly to the first century. It is a mocking image depicting a donkey-headed figure being crucified with a man standing before it next to the inscription "Alexamenos worshipping his God." So this anti-Christian graffiti is a couple of centuries older than the Christian bible (committed as a whole in the 4th century) and is as old or older than individual books in the New Testament.
A bit more foggy in my mind: Some years ago I read a transcript of some sort of Roman official's (no one huge in history, otherwise I'd remember his name) letter "debunking" Christ's divinity by outlining a "plausible" narrative that Jesus of Nazareth merely learned sorcery from the Egyptians and fooled the Jews into thinking he was a god.