He was first mentioned in a 1048 deed issued by the Salian emperor Henry III as a count in the Swabian Sisgau on the High Rhine (in present-day Northwestern Switzerland), an estate then held by the Prince-Bishopric of Basel.

[1] Rudolf's family had large possessions up to Sankt Blasien Abbey in the Black Forest and down to the Aargau beyond the border with the Kingdom of Burgundy.

[2] Rivalling with the Zähringen count Berthold, Rudolf, according to Frutolf of Michelsberg, had taken advantage of the minority of Agnes' son Henry IV, elected King of the Romans, by kidnapping his sister Matilda of Swabia.

In the 1062 Coup of Kaiserswerth, several princes led by Archbishop Anno II of Cologne even abducted the minor king to enforce the surrender of the Imperial Regalia.

[6] Finally when the Investiture Controversy broke out and King Henry was excommunicated by Pope Gregory VII in February 1076, Duke Rudolf met with Berthold, Welf and several other princes in Trebur in order to decide on a course of action and to arrange a new election.

Henry, observing the proceedings from his camp in Oppenheim on the other side of the Rhine, had to face a massive loss of support among the German nobles and realized that he had to achieve the lifting of his ban.

Duke Rudolf attempted to have the Alpine passes closed, nevertheless the king through wintry weather made his Walk to Canossa, where Gregory, fearing an armed attack by Henry's forces, had found refuge with Matilda of Tuscany.

[8] Rudolf gave Swabia to his son Berthold and attempted to rectify his situation by stalking Henry's forces near Würzburg, but to little effect.

The Battle of Mellrichstadt on 7 August 1078 proved indecisive: though the opposition forces under Otto of Nordheim were victorious, the troops of Berthold and Welf were stuck in a peasants' revolt.

The majority of the support for the rebellion against Henry IV soon evaporated, but the struggle continued on in effect into 1085, with a final flare up in 1088 under Rudolph's successor, the second anti-king, Herman of Luxembourg.