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On 10 April 1964, the famously eccentric concert pianist Glenn Gould retired from live performance at the age of 31. One of the most celebrated pianists of the 20th Century, Gould was a reclusive figure celebrated for his unusual interpretations - and also his habit of humming along with his own performances. John Roberts was one of his friends.

(Photo: Canadian pianist-composer Glenn Gould rehearsing with an orchestra at the Royal Festival Hall, London for a series of Beethoven concertos, using a piano stool only a few inches from the floor. Credit: Keystone/Getty Images)