Yes, that is why the question is aimed at atheist, I know how an agnostic would answer it.
Personally, as an agnostic, I am guessing, based on the lack of evidence, that either his character is based on a real person, who had great charisma, incredible goodness of heart, and who was probably a good magician, or is just a creation of the oral tradition.
Now way in the future, say some sufficient evidence is excavated to prove that Jesus was a real historical man, like Gandhi, or MLK, that I think will sit fine with atheists. Because his existence doesn't necessarily have to mean that God exists, because it's almost impossible to know his divinity.
It's also interesting how some of you guys brought up the existence of God. I was interested in Jesus as a human, not whether on the subject of the divinity of Jesus. That's a whole another ball game