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.
("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".)