Gregory XI was the pope who, after the greater part of a century, moved the papacy back to Rome. Although a Frenchman himself, he was convinced by the entreaties of Catherine of Siena.

This didn't go down well with the French faction: when Gregory died they set up a new, competing pope, back in Avignon. This era, with two combatative seats of power, is known as the Western Schism. By the end of it, a third papacy was set up in Pisa as well - but only the Roman popes are deemed to be legitimate by today's church. And since I'm following their list, I won't be drawing popes from the other sides of the Schism.