Paul wrote letters to communities of Christians throughout the Empire who evidently already knew some things about Jesus such as he was crucified and was called Son of God. One gets the strong impression that there was some Jesus-oriented belief system in place before Paul, including practices like baptism and moral system that was apparently Jewish law.
Paul appears to say that as Saul he persecuted those who followed Jesus. You may also be aware of the
>Gabriel's Vision stone<, which dates to the later 1st century BCE and at one point refers to an angelic leader who will die and rise again after three days. This may indicate the existence of a cult within Judaism with similarities to Christianity earlier than the traditional dates, and if that were correct, perhaps protoChristianity itself. It would also make the figure of the historical Jesus more elusive and perhaps more allusive.
If we take the traditional dates for the crucifixion around 30 AD and Paul’s letters being written in the 50s, the concept of a real Jesus having started some kind of religious movement, getting killed for his troubles, and the movement spreading after his death seems entirely reasonable.
My reading supports dating Paul's letters to the 50s. But the fact and date of the Crucifixion depend on the existence of a real Jesus. I think there's no clincher either way to that question. And whether there was a real Jesus or not, the earliest we meet Jesus in history is with Paul's letters, and Paul never met Jesus and has no clue about the earthly biography of Jesus ─ that he was a Jew, preached in Jerusalem, instituted the Last Supper (which in fact is a Greek borrowing) and was crucified and buried. Even after visiting 'James the brother of the Lord' and the Jerusalem Christians for a fortnight he has added not one biographical datum to his knowledge.
He also quotes what some scholars think is the earliest Christian document (if Gabriel's Vision is not): the 'kenosis hymn' in Philippians 2:5-11. It is (I read) written in poetic meter, and in verse 8 the phrase 'even death on a cross' appears to be a later gloss, since it breaks the meter. This raises the possibility that the crucifixion is a later part of the story, or that two stories are combined. And in verses 9-10 it says Jesus was not called Jesus ('Yeshua', old 'Yehoshua', the same name as Joshua, meaning 'Yahweh is salvation') until after his death.
There's only one biography of Jesus, that in Mark (about 75 CE). Imagine the wife of Mark's author comes home and finds her husband, pen in hand, staring at a blank sheet of paper. What are you doing? she says. I'm trying to write a biography of Jesus, but no one has any facts about him: I'm going nuts. She kisses him sweetly on the forehead and says, That's easy! Make a list of things that look like messianic prophecies in the Tanakh and have him perform them one after another. Then you can fit in the sayings on your other list! And he smiles widely and goes to get his Tanakh.
There may be some biographical clues to a real Jesus in there nonetheless. With only one exception, Jesus is sharply antagonistic to his family and to his mother every time she's mentioned (Mark 3:31, Mark 6:3, Mark 15:40, Matthew 10:35, Luke 11:27. John 2:3, contrast John 19:26). And it may be that Jesus was of puny build or had some visible disfigurement that would account for Luke 4:22 ('Physician, heal yourself'). Nor would the 'King of the Jews' sign as a piece of mockery work if Jesus had Arnie's build. But perhaps those elements are in the story because Isaiah 53:2 is taken as a prophecy for the messiah to fulfill.
A real Jesus seems to be the most likely explanation, although not the supernatural agent described in the NT.
As I said, I think it's a 50-50 chance: there may have been an historical Jesus or there may not have been; none is essential to account for what we know.