Rudolf of Rheinfelden (c. 1025 – 15 October 1080), a German aristocrat, was the Duke of Swabia (1057–1079), a brother-in-law of the Emperor Henry IV and the king-elect of a faction of the nobility in opposition to Henry from 1077. His election as King of Germany marked the outbreak of the Great Saxon Revolt, the first phase of open conflict in thecontest between Empire and Papacy over the issue of episcopal investiture. Rudolf died as a result of battlefield injuries after his forces defeated Henry"s at the Battle of Elster.