The problem in the OP is you cannot "prove" most ancient people. Most of the time we only have information allegedly from them or from others many years after them. Hammurabi is such an example...we have his alleged code...but how do we know someone just didn't claim to be Hammurabi? Se what I mean? Now I certainly believe in Hammurabi because I see no reason to believe he was not a real person. So why would one think Job was not a real person? What proof is there he may not have been? Same with Alexander the Great, who would doubt he was real? But "proof"? Not much I can tell you that. Most of what we know about him is from 100s of years after his death.