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Karas was an Austrian who played the zither. He was playing in a Vienna tavern when British director Carol Reed heard him and decided to have him score and play for the soundtrack of the film he was then shooting in Vienna, The Third Man. This was a brave decision by the director as Karas had absolutely no experience in composition or film scoring.
This was the first #1 in the USA for an Austrian.
Karas followed up with an album of his own pieces and other Viennese songs on Decca. He used his earnings from the film and recordings to buy a wine bar in Grinzing called "The Third Man." (thanks, Edward Pearce - Ashford, Kent, England, for all above)