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 Emperor and Papacy. After a series of armed conflicts, Rudolf succumbed to his injuries after his forces defeated Henry's in the Battle on the Elster.

Rheinfelden is a municipality in the canton of Aargau in Switzerland, seat of the district of Rheinfelden. It is located 15 kilometres east of Basel. The name means the fields of the Rhine, as the town is located on the High Rhine. It is home to Feldschlösschen, the most popular beer in Switzerland. The city is across the river from Rheinfelden in Baden-Württemberg; the two cities were joined until Napoleon Bonaparte fixed the Germany–Switzerland border on the Rhine in 1802 and are still socially and economically tied.