After his resurrection, Jesus told Peter his apostle to "Feed my sheep". He was the only one Jesus gave this kind of command to specifically, rather than in a group. Peter and the rest of the original apostles then went out and preached Christianity. Tradition has it that Peter was in Rome and was bishop there as head of the Christian church, since Rome was the head of the Empire, and then martyred. The popes trace themselves back from Peter and the popes are in charge. So if you look back, you could say Jesus founded Catholicism.

I'd say the man that founded Roman Catholicism was the Roman Emperior Constantine. I honestly do not believe that it was the Church that the Lord Jesus founded and I don't see how Peter could have been the first Pope if he was married since, as far as I know, the Catholic religion teaches that the popes are to be celibate. I hope that this is helpful. Thank you and God bless you!

Who founded the Catholic Church? Scripture tells us that the Church is built on the foundation of the Apostles. Christ called Simon Peter, the rock on which He would build His Church. Notice the future tense which is also present in the Greek. (Note also that the original text was probably not Greek as evidenced by multiple sources in the first couple of centuries that refer to Matthew's Gospel to the Hebrews written in the Hebrew language.) The fact that Christ says that He will build His Church indicates that the Church will be more than a loosely organized body of believers, which was already present, and that it will be an earthly Church. There is great example of the early Church (pre Council of Nicea) already being well organized and ruled by the Apostles and their ordained successors. For example, letters from Clement, the third Bishop of Rome, were read throughout the Christian world from western Europe to India. The word Catholic was first used to describe the Church by Irenaeus, who described the Church and its teachings as universally authoritative to Christians. In fact in his great work, "Against Heresies" Irenaeus wrote that if one wanted to know what Christian teachings were true, He should look to the first and greatest Church, the Church in Rome founded by the two most glorious Apostles Peter and Paul. Was this written during the time of Constantine? No it was written one hundred and sixty years earlier. Was Constantine involved in the Catholic Church, yes. Did he have a role in the Council of Nicea? Absolutely. What does this mean for Christianity? Well for that answer one would have to study the Church at that time, and the Arian Heresy, which at one point in time gained control of nearly 3/4 of all Christians. I believe that the testimony of history shows clearly that Jesus Christ founded the Catholic Church on Peter and the rest of the Apostles, and that it was safe guarded by their successors through the power of the Holy Spirit. But don't take my word for it. Primary sources are available in a number of different translations. Read them compare them to Scripture and to what is being taught today. Pray and come to an honest answer.

At Pentecost 33 C.E., thousands of Jews and proselytes were anointed with holy spirit. These new Christians became “a chosen race, a royal priesthood, a holy nation, a people for special possession.” (Read 1 Peter 2:9, 10.) The apostles kept careful watch over the congregations of God’s people as long as they lived. However, especially after the death of the apostles, men arose who spoke “twisted things” in order to “draw away the disciples after themselves.” (Acts 20:30; 2 Thess. 2:6-8) They did draw many many after themselvs. Many of these men had responsible positions in the congregations, serving as overseers and later as “bishops.” A clergy class started taking shape, although Jesus had said to his followers: “All of you are brothers.” (Matt. 23:8) Prominent men who were enamored of the philosophies of Aristotle and Plato introduced false religious ideas, gradually replacing the pure teachings of God’s Word. In 313 C.E., this apostate FORM of Christianity was granted legal recognition by the pagan Roman Emperor Constantine. From that time on, Church and State began working hand in hand. The Catholic Church, as the counterfeit form of Christianity came to be known, became the official religion of the Roman Empire. Historians refer to pagan Rome as having been “Christianized” in the fourth century.  The last apostle, Paul, died around 100C.E. Between 100 and 300 C.E. A counterfeit Christianity started to take root. Even so, there was a small number of True Christians doing their best to worship God, but their voices were being drowned out. (Read Matthew 13:24, 25, 37-39.) 

Little known fact: Jack Catholic, for whom the denomination was named.

It has been my understanding that that person is lost in time of which it was founded, in the 300s.

Jesus Christ thru His apostles founded the Catholic Church. The first recorded mention of the Catholic Church was written in a letter by St. Ignatius, to a church in Smyrna. This was about 107-108 AD. He wrote "Wherever the bishop appears let the congregation be present; just as wherever Jesus Christ is, there is the Catholic Church. Letter of Ignatius of Antioch to the Smyrnaeans VIII". This was centuries before Constantine was born or some other "forgotten individual" existed in the 4th century. Here is a link to a biography of St. Ignatius. https://maryourmother.net/Ignatius.html