The term 'Name of Thirteen Popes' refers to the names of thirteen popes who have served in the Catholic Church. The two crossword solutions for this term are INNOCENT (8 letters) and LEO (3 letters). INNOCENT was the name of Pope INNOCENT III, who served from 1198 to 1216 and is considered one of the most influential popes in history. LEO was the name of Pope LEO XIII, who served from 1878 to 1903 and was the first pope to be photographed.