The textbook answer is someone who believes and follows the words and teachings of Christ, the historical figure known as Jesus who said among other things that he was the prophesied son of God, The God of the Jewish tradition and recorded in what Christians call the Old Testament. In my view, what makes a true Christian is not only believing and following Christ, but living your life to the fullest extent of what that means. The popular bumper sticker phrase, "What Would Jesus Do?" reflects a sentiment that I, in my view, feel too many self-described Christians fail to incorporate into their lives. Jesus was not just honest, and caring, and compassionate, but he practiced tolerance, he loved even the dregs of society, he had sympathy for the ostracized, the outcast, he basically gave everyone the benefit of the doubt. This, in my view, is a great irony, that the last thing Jesus would ever do, is judge someone for who they were, when he was in fact the son of the final judge and in many views sharing of all God's powers, including judgment. So he had the ability to judge, but refrained from it just the same. In my view this was his greatest example for future Christians.