Today in German History, Oct. 5th

Henry IV becomes emperor after the unexpected death of his father, Henry III. Henry IV is famous for his conflict with the papacy over the right of the emperor to invest churchmen with their symbols of office, generally called "the Investiture Crisis." His reign also coincides with the further demise of the stamm duchies and the development of the more feudal (a term with endless complications) lordship of those aristocrats whose names are derived from their castes, such as the Hohenstaufen and Hapsburg.

Arnold, Benjamin. Medieval Germany, 500-1300: A Political Interpretation. Toronto: University of Toronto Press, 1997. 

Blumenthal, Uta-Renate. The Investiture Controversy: Church and Monarchy from the Ninth to the twelfth Century, trans by the author. Philadelphia: University of Pennsylvania Press, 1988.