He is most famous for the role he played in the Investiture Controversy with Henry IV.
The politico-religious struggle between Gregory VII and Henry IV is known as the Investiture Contest (or sometimes the Investiture Controversy) but was not limited solely to Henry and Gregory - other Popes/ecclesiastical figures and aristocrats were involved - nor was it even limited to their lifetimes. The Investiture Contest was an 11th-12th century development, and part of what is now often referred to as the Gregorian Reforms. Hope that helps!
Pope Gregory VII checked the power of the Holy Roman Emperor by asserting the principle of papal supremacy, particularly through the famous Investiture Controversy. He opposed the practice of lay investiture, where secular leaders appointed church officials, claiming that only the pope had the authority to appoint bishops. This conflict culminated in the excommunication of Emperor Henry IV, which weakened his authority and led to a significant power struggle between the papacy and the monarchy. Gregory's actions reinforced the idea that the pope held spiritual authority over secular rulers.
The term is the Investiture Controversy,
The issue was the Investiture Controversy, the question of who had the right to choose new bishops.
Pope Gregory VII was one of the most prominent opponents of lay investiture during the Investiture Controversy in the 11th century. He believed that only the church had the authority to appoint bishops and saw lay investiture as an encroachment on the church's independence.
Pope Gregory VII clashed with and excommunicated the German emperor, Henry IV, during the Investiture Controversy in the 11th century. This conflict arose over the appointment of bishops and who had the authority to invest them with their symbols of office.
Henry wanted the right to name new bishops in his kingdom. Gregory stated that only the pope could elevate bishops. It became known as the Lay Investiture Controversy.
Pope Gregory VII, and Henry IV
An argument went on between Gregory and Henry. This argument was on whether Henry or Gregory should choose the next Bishop. Gregory got rejected by the Roman's on whether he should pick the next Bishop because of Henry. So Gregory "Excommunicated" Henry. Henry then traveled to Italy to apologize to Gregory. Before Gregory forgave him Henry stood out in the snow for three days out side of Gregory's room.
Roman Catholic AnswerThe issue was lay investiture, where the Emperor was filling the vacant sees of Bishops. Pope Gregory VII removed this power, when Henry refused to go along with him, Pope Gregory excommunicated him and all the bishops that he appointed it. However, Henry immediately submitted so the Holy Father had to reinstate him and give him penance.
In the course of the Investiture Controversy, Henry IV had be excommunicated. In order to have the ban lifted, he went to see the Pope at Canossa to do penance. He stood in the snow three days, begging to be forgiven. Popular legend has him doing this barefoot. He was forgiven, but required to meet certain conditions, which he violated, and the problems continued. There is a link below to an article on the Investiture Controversy.