[Responsibility2nd]

Many Bishops of Rome were first identified as Pontifex Maximus. A pagan term.

From there, the term Pope became more popular. A term, as we all know, is not found in the Bible.

[Campion]

The term "Pontifex Maximus"* was the title of the head of the Roman state religion. When Christianity became the state religion (under Theodosius the Great), the title naturally was transferred from the Emperor to the Pope.

("Maximus" is simply "greatest". "Pontifex" comes from the words for "bridge" and "builder". At least in later Latin, it's used as a generic term for a senior religious leader without regard to what religion is meant. For example, the Vulgate Bible calls the Jewish High Priest "Pontifex Iudaeis".)