This ruler agreed to allow the demolition of fortresses in the Treaty of Gerstungen, but fought the FirstBattle of Langensalza after his family's tomb was desecrated in the process. An enemy of this rulersupported Rudolf of Rheinfelden's ineffective rebellion against him and died hiding from him under theprotection of Robert Guiscard. After conquering Rome, he put Guibert 
This ruler agreed to allow the demolition of fortresses in the Treaty of Gerstungen, but fought the FirstBattle of Langensalza after his family's tomb was desecrated in the process. An enemy of this rulersupported Rudolf of Rheinfelden's ineffective rebellion against him and died hiding from him under theprotection of Robert Guiscard. After conquering Rome, he put Guibert of Ravenna on the papal throne asAntipope Clement III, taking revenge against a pope who excommunicated him even after he put on ahairshirt and walked barefoot through the snow. For 10 points, name this Holy Roman Emperor who tookthe "walk to Canossa" while clashing with Pope Gregory VII in the Investiture Controversy.
This ruler agreed to allow the demolition of fortresses in the Treaty of Gerstungen, but fought the FirstBattle of Langensalza after his family's tomb was desecrated in the process.
Henry IV of the Holy Roman Empire [or Henry VIII of Bavaria; prompt on Henry]