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Lev Sergeyevich Termen, also known as Leon Theremin, was a Russian inventor and musician best known for his creation of Theremin, an electronic musical instrument controlled by hand gestures. Born in St. Petersburg in 1896, Termen's interest in physics and electronics led him to develop Theremin in the early 1920s. The instrument gained international fame and was embraced by musicians and composers for its unique and ethereal sound.