The world would be a very different place without Leo the Great. His Tome was hugely influential at Chalcedon as were his opinions on Papal Authority upon later popes. Also, you have most of the Popes who were involved in the schisms with Constantinople that took place over the centuries, like Pope Hormisdas, whose absence would have done a lot to change East-West relations. There were those whose theology made sure there were less compromises with the Miaphysites, like Pope Agatho, whose absence would have seriously altered the politics of the Middle East before the coming of Islam. There was also Pope Nicholas I, who was an important player in the Photian Schism, which was one of the major reasons that there even was a break with Constantinople in 1054, let alone why it became permanent.
Unsurprisingly, being the head of what would one day become the world's largest body of organized religion means you often have a lot of influence on history.
Unsurprisingly, being the head of what would one day become the world's largest body of organized religion means you often have a lot of influence on history.