Gregory VII
c.1020 - 1085
Gregory - known as Hildebrand before he became pope - was the most eminent medieval pope. He asserted his supremacy with the demand that the pope had the right to depose an emperor if the monarch was immoral.

One of the great reforming popes, Gregory VII is best known for the part he played in the Investiture Controversy, his dispute with Henry IV, Holy Roman Emperor affirming the primacy of the papal authority and the new canon law governing the election of the pope by the college of cardinals.

He was at the forefront of both evolutionary developments in the relationship between the Emperor and the papacy during the years before becoming pope. As Pope he excommunicated the emperor Henry IV forcing him to travel to Canossa in Italy to plead for absolution.

www link :

The Medieval Sourcebook:
First Banning of Henry IV, 1076

The Gregorian Calendar