Who taught that Peter was the first pope?

Answer 1

Jesus Christ appointed Peter as the first leader of his Church when He said:

And Jesus answering, said to him: Blessed art thou, Simon Bar-Jona: because flesh and blood hath not revealed it to thee, but my Father who is in heaven. And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it. And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose upon earth, it shall be loosed also in heaven. (Matthew Chapt. 16)

Peter is considered the first pope even though the term 'pope' did not come into common usage until much later. Whether Peter was in Jerusalem, Antioch, Rome or elsewhere, he is still considered the first pope. Later, as the Church grew and a hierarchy developed. the Church established its headquarters in Rome as Rome was considered the center of the world at the time. It had good roads reaching out to the vast empire as well as ships that plied the Mediterranean. Missionaries could reach anywhere in the known world from Rome. As the pope was the highest ranking Church authority in Rome, he was automatically consider the Bishop of Rome.

Answer 2

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Catholic AnswerThat would be Our Blessed Lord, Jesus Christ, although the term "pope" was not used until centuries later. Our Blessed Lord raising of Peter to be His Vicar is contained in St. Matthew's Gospel, chapter 16, verses 17-19.