The Bible does not say who went to Rome to win converts to Christianity. However, Paul's Epistle to the Romans demonstrates that by the fifties at the latest, there was already a flourishing Christian community in Rome.
Paul is believed to have gone to Rome, but probably not with the intention of converting people to Christianity. Peter is traditionally thought to have moved to Rome, to head the church there, but there is no actual evidence that he ever visited Rome. Clement of Rome, while mentioning Peter, gives no hint that he knew of Peter having been in Rome a few decades earlier.
Paul.
Paul.
to convert many people to Christianity
He brought a priest from Norway with him to Greenland to help convert the people to Christianity.
missionaries
the Apostle Paul who was not one of the original 12 Apostles and the Apostle John, as well as the other Apostles and disciples, missionaries and church planters.
The Apostle Paul was one of the main people who ministered to the gentiles (non-Jews)
There was no one particular person who spread Christianity throughout the empire. All of the disciples/apostles of Jesus went out to "teach all nations". Several apostles are patrons of distant countries and they may very well have traveled to them. For example, James is affiliated with Spain, Peter with Rome, Luke, although not an apostle but a friend of Paul, is buried in Padua, Italy according to the latest DNA. Paul himself traveled and wrote throughout the middle east until he was taken to Rome as a prisoner. The Roman Emperor Constantine also helped spread Christianity by declaring it the official religion of the Roman Empire.
he and his people will convert to his christinanity
St. John Brebeuf came from France to convert Native Americans to Christianity. He came with other Jesuits & they were subsequently Martyred in the New World.
They had been outcasts, but the church accepts them.
Charlemagne forced the conquered peoples to convert to Christianity.