Where does the book of Job come from?

What I mean is the following: - Job stands out as being as old as the Torah (if not older) - None of the characters are Israelites (especially if it was Abrahamic time when Israel didn't even exist) - Every other book can be traced back by tradition, the author is fully unknown So how did the Jews get a hold of Job scriptures? or does it not have an answer and is left to theory?