Berthold I, Duke of Swabia

Berthold I (c. 1060 – 18 May 1090), better known as Berthold of Rheinfelden, was the Duke of Swabia from 1079 until his death. He was the oldest son of Rudolf of Rheinfelden,the youngest being Otto, the German anti-king who opposed the Emperor Henry IV.

Berthold's mother's name is unknown, but on her death in 1079, Rudolf needed a new supervisor of the south German resistance, since he was himself confined to Saxony and cut off from his allies in Swabia. Rudolf therefore made his son Duke of Swabia. Henry, however, appointed Frederick of Büren, who had lands strategically located much to his advantage, Duke.

Throughout the civil war against Henry, Swabia was in the heart of the chaos. In 1084, Berthold was besieged by supporters of Henry IV. Though he had a larger power base, he remained of low profile. He eventually left the fight to Berthold of Zähringen and Welf IV. When he died without descendants in 1090 and was buried in the monastery of Saint Blaise, Berthold succeeded him as duke.