On Earth, the Pope was a title given to the religious leader who led the Roman Catholic branch of Christianity on Earth. Over the centuries since the founding of the office the Pope was an influential part of world affairs. The Pope had his headquarters in the Vatican City, a part of Rome, Italy.
In the early 13th century, disagreements between Pope Innocent III, King John of England, and the various members of the English nobility led to the creation of the Magna Carta. The Magna Carta eventually came to be considered one of the first step of the process in Earth history leading to the rule of constitutional law. (TOS episode: "Court Martial")