Rudolf of Rheinfelden (also Rudolf of Swabia), died October 15, 1080, was Duke of Swabia (1057–1077) and German Antiking (1077–1080). He was the son of Count Kuno of Rheinfelden.

In 1057 Rudolf took advantage of the minority of German King Henry IV by kidnapping Matilda, daughter of the dowager empress Agnes of Poitou, Henry's mother. Rudolf demanded, and received, Matilda's hand in marriage (1059), as well as the Duchy of Swabia and administration of the Kingdom of Burgundy. In 1060 Matilda died, and Rudolf remarried in 1066 to Adelheid, daughter of Otto of Savoy.

Rudolf, who was a brother-in-law to Henry, at first supported the king's campaigns. He helped him in Thuringia and Saxony and was a primary force in the First Battle of Langensalza against the rebels. However, when the Investiture Controversy broke out and Henry was excommunicated, Rudolf met with several other nobles to decide on a course of action. Despite the lifting of the excommunication in 1077, the revolters continued with their plans. At Forchheim, Rudolf was elected antiking in March. He promised to respect the electoral concept of the monarchy, and declared his willingness to be subservient to the pope.

In May Rudolf was crowned at Mainz, but the people of the city revolted and he was forced to flee to Saxony. This presented a problem, since Saxony was cut off from his duchy of Swabia by the king's lands. He then gave Swabia to his son Berthold and attempted to rectify this situation by sieging Würzburg, but to little effect. Meanwhile, Swabia was deprived of him by the Diet at Ulm in May, and Henry gave the duchy to Frederick of Büren, the first Hohenstaufen ruler.

The following year, the battle of Mellrichstadt (August 7), proved indecisive. Rudolf found difficulties in convincing the Saxons to fight beyond their borders; they viewed Rudolf as a southerner and distrusted him. He was also frustrated by the apparent reluctance by the pope in recognizing his cause. In order to gain and maintain supporters, he was forced to grant large parts of the crown lands, as well as those of the church. Nevertheless, things seemed to be improving in 1080. The battle of Flarchheim (January 27, 1080) went well in his favor. On March 7, the pope finally excommunicated Henry again and recognized Rudolf as king.

Emboldened, his forces met Henry's at the Elster River . The battle, which took place on October 15, would have been a huge victory for the anti-royalists. However, in the battle Rudolf lost his right hand and was wounded in the abdomen. Withdrawing to nearby Merseburg, he there died. The anti-royalist cause soon deteriorated, with no one able to to replace Rudolf.