As an agnostic atheist who grew up in a non-religious (well, both my parents were lapsed Catholics) household, I always assumed Jesus existed, but was probably just a cult leader with a small group of followers and Christianity grew around him after his death like he was a piece of grit in an oyster shell.

Except there’s really no way to prove he existed because two millennia of Christian attempts to find (and make) evidence that he was a real person have thoroughly muddied the waters and also, over 2,000 years, there are famous people we know existed because of historical records but don’t have any of their possessions, writings in their own hand, portraits painted from life, etc.