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 eldest 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.

Throughout the civil war against Henry IV, Swabia was thrown into chaos. In 1084, Berthold, Duke of Swabia, was besieged by supporters of Henry IV. Although he had a larger power base, he was of lower rank. 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.