Pope Leo IX
Head of Catholic Church (1049-1054)
The instrumental figurehead of the Catholic Church in charge during the Schism. He is recognized as a saint within the Catholic Church. Upon becoming Pope, Leo implemented celibacy all the way down to subdeacon. Soon before he passed Leo sent a proxy to negotiate with Michael after denouncing the pope. Pope Leo died somewhere during the proxy's time of arrival making his wishes invalid. The proxy instead delivered excommunications to the patriarch and was met by Michaels own excommunication. This is considered the official split between the East and West churches.
Patriarch Michael I Cerularious
Patriarch of Constantinople (1043-1059)
Michael I Cerularious of Constantinople had just as much of a part in this Schism as Pope Leo IX. Michael was not a fan of Pope Leo IX to put it bluntly. He had multiple issues with different practices in the Roman Church versus the Constantinople. One of them being his issue with the Pope being the supreme ruler of the Church. Michael refused to meet with the papal proxy that came to discuss with him which led to the mutual excommunication which led to the Schism.