Rudolf of Rheinfelden was Duke of Swabia from 1057 to 1079. Initially a follower of his brother-in-law, the Salian emperor Henry IV, his election as German anti-king in 1077 marked the outbreak of the Great Saxon Revolt and the first phase of open conflict in the Investiture Controversy between the Emperor and the Papacy. After a series of armed conflicts, Rudolf succumbed to his injuries after his forces defeated Henry's in the Battle on the Elster.