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Who was Rudolf of Rheinfelden and why did Gregory VII recognize him as king?

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Gregory VII excommunicating Henry IV — St. Gregory VII Pope Gregory VII, after his expulsion from Rome, laying a ban of excommunication on the clergy “together with the raging king” (Henry IV of Germany), drawing from the 12th-century chronicle of Otto of Freising; in the library of the University of Jena, Germany.

Rudolf of Rheinfelden was a German nobleman and the Duke of Swabia who became an anti-king in opposition to Henry IV during the Investiture Controversy.12

Following the excommunication of Henry IV by Pope Gregory VII, German princes opposed to the king elected Rudolf as their ruler in March 1077. While Gregory VII initially attempted to arbitrate between the two parties, he eventually recognized Rudolf as the legitimate king early in 1080.13

Gregory’s decision to formally recognize Rudolf was driven by the escalating conflict between the papacy and Henry IV. This tension was rooted in Gregory’s reform efforts, specifically his prohibition of lay investiture, which Henry IV refused to obey. By supporting Rudolf, Gregory sought to challenge Henry’s authority and assert the primacy of the papacy over secular rulers in both spiritual and political spheres.32