Like many elements of the Universal(Catholic) Church, its practices are founded on tradition. Traditionally, when one becomes completely consecrated (given over) to God (among other things: conversion, ect.), one takes a new name. It is a long standing tradition that the Pope, as Vicar of Christ, shepherds the entire Church and is thus completely given over to her. The Pope usually takes a name of one of his predecessors, sometimes used to hint at the type of papacy he will be taking inspiration from or attempting to follow in the footsteps of.
The Black Pope's birth name is Shelly Pope.
Alece Pope's birth name is Charlotte Alece Pope.
Cassadee Pope's birth name is Cassadee Blake Pope.
Dennis Pope's birth name is Dennis Allen Pope.
Eddie Pope's birth name is George Edward Pope.
Edwin Pope's birth name is John Edwin Pope.
Everett Pope's birth name is Everett Parker Pope.
Katherine Pope's birth name is Katherine Collins Pope.
Marquez Pope's birth name is Marquez Phillips Pope.
Tommy Pope's birth name is Thomas Elbert Pope.
Julie Pope's birth name is Julie Smith.
Lynne Pope's birth name is Patricia Lynne Parker.