Final answer:
Ken's belief that he is the Pope is an example of a grandiose delusion. The Pope's role in history includes religious and temporal authority, notably strengthened during the investiture controversy under Pope Gregory VII.
Step-by-step explanation:
The question posed about Ken believing he is Pope of the Catholic Church and his insistence on returning to Rome to resume his duties is an example of a delusion, specifically, a grandiose delusion. A delusion is a firm and fixed belief in something that is not based in reality. In the context of the Catholic Church, the Pope serves as the spiritual leader and has a significant historical role that includes both religious and temporal authority over the Church's matters. Over the centuries, the role of the Pope evolved from an emphasis on spiritual leadership to also having significant political influence, commanding armies, and having the ability to affect monarchs and political landscapes.
Pope Gregory VII's actions during the investiture controversy in the 11th century were instrumental in cementing the power of the Pope by banning the practice of simony and establishing that the Pope, not secular rulers, had the ultimate authority over church officials. This consolidation of power ultimately gave the Pope substantial influence over the spiritual and temporal realms.