Sadly, I would answer Constantine. At the beginning of his career, Constantine needed some “divine” patronage, and this could not be provided by the fading Roman gods. The empire, including its religion and other institutions, was in decline, and something new and invigorating was needed to reconsolidate it. The encyclopedia Hidria says: “Constantine was especially interested in Christianity because it backed up not only his victory but also the reorganization of his empire. The Christian churches that existed everywhere became his political support. . . . He surrounded himself with the great prelates of the times . . . , and he requested that they keep their unity intact.” Constantine sensed that the “Christian” religion, albeit apostate and deeply corrupted by then, could be effectively utilized as a revitalizing and uniting force to serve his grand scheme for imperial domination. Adopting the foundations of apostate Christianity to gain support in furthering his own political ends, he decided to unify the people under one “catholic,” or universal, religion. Pagan customs and celebrations were given “Christian” names. And “Christian” clergymen were given the status, salary, and influential clout of pagan priests. Seeking religious harmony for political reasons, Constantine quickly crushed any dissenting voices, not on the grounds of doctrinal truth, but on the basis of majority acceptance. The profound dogmatic differences within the badly divided “Christian” church gave him the opportunity to intervene as a “God sent” mediator. Through his dealings with the Donatists in North Africa and the followers of Arius in the eastern portion of the empire, he quickly discovered that persuasion was not enough to forge a solid, unified faith. It was in an attempt to resolve the Arian controversy that he convened the first ecumenical council in the history of the church. When you look around the world today, and see that roughly one third of the world's inhabitants call themselves "Christians", then you can see just what a corrupting influence that Constantine had. If one third of the people on earth were truly living as Christians should, the world would be a much better place than it is.

considering almost half of the New Testament was written by Paul, and that the whole reformation thing was, in large part, a result of Martin Luther reading Paul's writings, it would have to be Paul. _________________________________ Also, if you read Acts 16 you would see that it would have been highly unlikely that Christianity would have ever left Israel had it not been for Paul. Therefore without Paul, Constantine never would have made Christianity an official religion. It is debated whether Constantine even was a Christian. Many people believe his action was done primarily because of the number of Christians already present and that it was a purely political manuever (as we have records of several hundreds of thousands Christians in the empire at the time spread throughout the entire region).

I have to agree with perryman, Constantine I feel had the greatest impact on Christianity for a very simple reason. If it wasn't for the fact that Constantine (and therefore following emperors) made Christianity the official religion of Rome, everything that Paul wrote may have simply continued as just another of the many beliefs that circulated around Rome back then. The adoption of the Chrisian faith by Rome gave the faith a huge push into the known world, in many cases forcing the Pagan faiths into the background as it took over as the only official Roman faith. Until that time, Pagan beliefs dominated Rome and almost every other country so without the official backing that started with Constantine it may never have gotten past the small gathering of followers Paul had. Although, it is interesting that Constantine was not actually baptised until he was on his death bed and, whilst he claimed to be Christian, he held the position of Pontifex Maximus, which at that time was the Pagan High Priest (you can see the massive influence Roman Pagan religion had on early Christians when you consider that the title for the head of the Roman Catholic Church, the Pontifex Maximus, was originally the Pagan High Priest heading up the (Pagan) College of Pontiffs!)

Constantine. If he hadn't spread Christianity so far and wide with his empire, very few people would know who Paul is or what he wrote (which isn't necessarily a bad prospect).

Constantine. He is called the 13th apostle, the Head of the Church, Pontifex Maximums (the high priest). He changed the early face of Christianity. And he is the founder of Today Christianity. The Creeds, the Trinity, deity of Jesus, Sunday, charismas, the Easter etc all are the fruits of the great Emperor.

Paul initially, one of the obvious....Constantine's conversion was God's way of taking over the Roman Empire to establish his Church. This is why Christianity is the predominate religion in our modern world. All forms of Christianity came from the Catholic Church.

not sure