John remains the most popular papal name in the history of the Catholic Church, followed by Gregory, Benedict, Clement, Innocent, Leo, and Pius.
Apart from Landus, John Paul I and Francis, other popes may have wished to pick a unique name, but their choice was considered incongruous or unappropriate.
It is said that John Paul II, born with the name Karol Wojtyla, had initially chosen the name Stanislaw, out of respect for the patron saint of his native Poland. The cardinals would have dissuaded him, as the name did not belong to the Roman tradition.
PHOTOS: Inside the Sistine Chapel
In other cases, the chosen name, even if was previously used, wasn't just considered appropriate.
The vain Pietro Balbo, who became Paul II, wished to adopt the name Formosus II for his election in 1417. Meaning "beautiful" in Latin, the name wasn't however the best one to invoke as it would have reminded the so-called Cadaver Synod, where Pope Formosus I, exhumed nearly a year after his death, was put on trial by his successor Stephen VI.