After Paul of Tarsus, would Constantine I be the next most import person in the spread of Christianity?
Yes.
Paul of Tarsus? Is that like Muhammad Clay?
Agreed.
I don’t get it.
Another vote for Constantine in second place.
Other contenders would be Augustine, Pope Gregory, and Theodosius.
Wasn’t it already pretty widely spread when Constantine made it the religion of the state? Altthough of course he’s hugely important in keeping it that way. More important figures in the actual spread of Christianity though than that Emperor would be the missionaries who later converted the Germanic and Gothic tribes that overran the Empire. But for their work we could all be worshipping Odin!
Constantine didn’t make Christianity the state religion. He legalized Christianity and showed it personal favoritism.
It was Theodosius who made Christianity the state religion of the Empire.
I believe the point is that he was originally known as Saul of Tarsus, later as Paul the Apostle. You’ve combined the first and last parts of two different names, like taking Muhammad from “Muhammad Ali” and Clay from “Cassius Clay”.
I think Doug K. is alluding to Paul’s name change as a result of religious conversion.
Cassius Clay changed his name to Muhammad Ali after he converted to the Nation of Islam; Saul of Tarsus, a Jewish Pharisee, changed his name to Paul after Jesus appeared to him and he was converted to Christianity.
So referring to “Paul of Tarsus” is conflating the pre-conversion name with the post-conversion name, in much the same manner as would calling the boxer, “Muhammad Clay.”
You beat me to posting while I was typing, dang it! (I’m a really slow typist with a tendency to multitask) 
Yeah, it came to me later on. A bit of a stretch for a joke. Paul of Tarsus is perfectly acceptable as a reference to Paul the Apostle.
I agree (except for the making it the religion of the state part)…his function was one of legitimization and influence on its administration rather than evangelism. Further, he had a permissive attitude toward many religions, not just Christianity. While he lent legitimization to this religion, he was not the first emperor to order an end to Christian persecution (Galerius, before him), nor did he make Christianity the state religion…that happened under a later emperor, Theodosius I. There are varying claims Constantine converted to Christianity at some point in his life (or on his deathbed), but there is no good evidence this ever actually happened. If you’re looking for people who spread it geographically after Paul, I would consider the early church theologians. Although, I think their writings traveled more extensively than they actually did themselves. You might also look into the Sator Square. Personally, I think the evidence is pretty good that was likely a Christian symbol and it spread far and wide during the period Christians were persecuted.
Let’s not forget Constantine’s mother Helena. By all accounts she was a major influence in his conversion.
Not I!
Thanks, St Pat. There probably really was a Patrick–although many legends have overlain the man. He wasn’t the only missionary to the Irish–or even the first. In turn, the Irish missionized many of the heathen Germans. And even some of the Saxons on That Other Island…
Does God even make it in the top ten?
Spoken like a true Irishwoman.
Not on a list of the most important people.
He should if you believe in the sanctioned Trinitarian doctrine. God the Son is fully human and fully God. No Jesus, no spread of His teachings.
It was, which was a big factor in his decision to cosy up to it. On the other hand, his cosying-up did give it a big boost, and was undoubtedly a factor in Christianity becoming signficantly more widespread than it already was.
Yes, but I think the OP is looking for individuals. The missionary spirit inherent in Christianity, and expressed both by individuals and by organisations, is undoubtedly a bigger factor than Constantine. But Constantine is a person.