Kerstin Thorborg (19 May 1896 â 12 April 1970) was a Swedish opera singer. The Mezzo-soprano Kerstin Thorborg was one of the best dramatic Wagnerian singers in the two decades between 1930 and 1950. By all accounts, Thorborg was a magnificent actor with great stage presence. In addition, she was endowed with a beautifully steady and intense tone.