How can you prove that he was the first Pope?

The word Pope means Father or Head of the Church as an ordinary father is head of a family. St. Peter was certainly in Rome, and died there as Bishop. By legitimate succession the one who succeeded as Bishop of Rome after Peter’s death inherited the office of Head of the Church, or if you wish, as Father of the whole Christian family he was Pope. All the Bishops of Rome right through the centuries have belonged to the Catholic Church. No one disputes that. They are known as the Popes, and as St. Peter was first of that long line, Catholics rightly regard him as the first Pope.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty