He was possibly the descendant of one Berthold (Bezzelin) of Zähringen, a Swabian count in the Breisgau region and relative of the Ahalolfing dynasty who was killed in the 982 Battle of Stilo fighting against the Kalbid emir of Sicily. On his mother"s side of the family, Berthold probably descended from the House of Hohenstaufen, who then were counts in Ortenau, Thurgau, Breisgau, and Baar.
However, upon Otto"s death in 1057, Henry"s widow Agnes of Poitou gave Swabia in fief to Count Rudolf of Rheinfelden. Berthold received, as compensation for the abandonment of his claim, the ducal titles to Carinthia with the Veronese march after the death of the Ezzonid duke Conrad III in 1061, whereby the Zähringer finally ascended to the status of a princely house. In Carinthia and Verona, though, Berthold like his predecessor was considered a foreign ruler and never really accepted by the local nobles.
According to the contemporary chronicler Lambert of Hersfeld, he was even temporarily declared deposed in 1072/73.
In turn, the king on the Imperial Diet at Ulm seized his duchy and gave Carinthia to Liutold of Eppenstein. Berthold retired to his Swabian home territory, where he had to ward off constant attacks by King Henry"s forces.
He died the next year at Limburg Castle and was buried in Hirsau Abbey, where he had backed the erection of the monastery church under Abbot William.
