'Finally there is the key contributor who became known as the Fourth Man: zither-player Anton Karas, who was playing when Reed and his team first had dinner at the Astoria. Reed was much taken with Karas’s playing and, to Korda’s surprise, the director proposed that instead of a conventional orchestral score, The Third Man be accompanied by Karas’s solo zither alone. The music scored a huge hit — and Karas, in demand around the world, was able to provide amply for his family.'

https://www.ft.com/content/e7c59b93-2536-44c8-947b-de6c3e904f88