When Duke Otto III of Swabia died without male heirs in 1057, Empress Agnes, consort of late Henry III, appointed Rudolf Swabian duke and administrator of Burgundy. 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. Rudolf demanded, and received, Matilda's hand in marriage (1059). In 1061 Berthold received the Duchy of Carinthia instead. When Matilda died in 1060, Rudolf subsequently, in 1066, married Adelaide of Savoy (d. 1079), a daughter of Count Otto of Savoy and Adelaide of Susa. When Adelaide's sister Bertha of Savoy married Henry IV in 1066, Rudolf became brother-in-law to the king twice over.