There were Christian churches before the Apostle Paul even did his first missionary journey: this from roughly 0040 AD:

Acts 11:25-26 Then Barnabas went to Tarsus to look for Saul, and when he found him, he brought him back to Antioch. So for a full year they met together with the church and taught large numbers of people. The disciples were first called Christians at Antioch.

Christians were persecuted from the stoning of Stephen in ~0035 AD until Constantine made it the official religion of the Roman empire in the early 300's. But there were many famous Christians prior to that. For example:

Clement of Rome The epistle known as 1 Clement (c. 96) is attributed to this early bishop of Rome. It was widely read in the churches and is considered the earliest Christian epistle outside the New Testament. Tradition identifies Clement as the fourth pope.

Ignatius of Antioch (c. 35-110) was the third bishop of Antioch and a student of the Apostle John. En route to his martyrdom in Rome, Ignatius wrote a series of letters to various churches, and these have been preserved as an example of the theology of the earliest Christians. Important topics addressed in these letters include ecclesiology, the sacraments, and the central role of bishops in authorized orthodox teaching.

Polycarp (c. 69-c. 156) was the bishop of Smyrna (now İzmir in Turkey). In 155, the Smyrnans demanded Polycarp's execution as a Christian, and he died a martyr. He was also an important figure in the controversy over the date on which Christians celebrate Easter.

Clement of Alexandria (c. 150-211/216), was a distinguished teacher in the city which became one of early Christianity's most important intellectual centers. He united Greek philosophical traditions with Christian doctrine and thus developed what later became known as Christian Platonism.

Origen (c. 185 - c. 254) also taught in Alexandria, reviving the catechetical school where Clement had taught. He interpreted scripture allegorically and further developed the tradition of Christian Platonism. Origen taught a doctrine of universal salvation in which even demons would eventually be reunited with God. Although some of his views were declared anathema in the sixth century by the Fifth Ecumenical Council,[2] Origen's thought exercised significant influence.

Irenaeus of Lyons (d. near the end of the third century) was bishop of Lugdunum in Gaul, which is now Lyons, France. A disciple of Polycarp, his best-known book, Against Heresies (c. 180), enumerated heresies and attacked them. Irenaeus wrote that the only way for [Christian]s to retain unity was to humbly accept one doctrinal authority of orthodox bishops, with disputes resolved by episcopal councils. His work is a major source for understanding the heterodox movements of the second century and the orthodox churches' attitude in combating them.

Athanasius of Alexandria (c. 293-May 2, 373), also known as St. Athanasius the Great, was a theologian who later became the patriarch ("pope") of Alexandria, a leader of immense significance in the theological battles of the fourth century. He is best remembered for his role in the conflict with Arianism, although his influence covers a vast array of theological topics.

Tertullian Quintus Septimius Florens Tertullianus (c. 160-c. 225) was a prolific writer of apologetic, theological, anti-heretical, and ascetic works. He is believed to have introduced the Latin term "trinitas" (Trinity) to the Christian vocabulary and also the formula "three persons, one substance"—tres personae, una substantia. Later in life, Tertullian joined the Montanists, a heretical sect, but his writings by and large are considered as a shining example of orthodoxy.

Cyprian (died September 14, 258) was bishop of Carthage and an important early Christian writer who eventually died a martyr at Carthage. He is particularly important in defining the Christian church as "Catholic," meaning "universal," and his insistence that there can be no salvation outside of the Christian church.