Léon Theremin (born Lev Sergeyevich Termen, Лев Сергеевич Термен in Russian) (August 15 1896–November 3 1993) was a Russian inventor, most famous for his invention of the theremin, one of the first electronic musical instruments.
Léon Theremin was born in Saint Petersburg. His invention in 1919 of the theremin (also called the thereminvox) came at a time when his country was in the midst of the Russian Civil War. After a lengthy tour of Europe, during which time he demonstrated his invention to packed houses, Theremin found his way to America, playing the theremin with the New York Philharmonic in 1928. He patented his invention in 1929 (US1661058 ) and subsequently granted commercial production rights to RCA.
Léon Theremin set up a laboratory in New York in the 1930s where he developed the theremin and experimented with other electronic musical instruments and other inventions, including the Rhythmicon, commissioned by the American composer and theorist Henry Cowell. In 1930, ten thereminists performed on stage at Carnegie Hall and, two years later, Léon conducted the first-ever electronic orchestra, featuring the theremin and other electronic instruments including a "Fingerboard" theremin which resembled a cello in use. Theremin's mentors during this time were society's foremost scientists, composers, and musical theorists, including composer Joseph Schillinger and physicist (and amateur violinist) Albert Einstein. At this time, Theremin worked closely with fellow Russian émigré and theremin virtuoso Clara Rockmore.
Determined to establish his instrument in mainstream scientific and musical settings, Léon was interested in the role of the theremin in dance music. He developed performance locations that could automatically react to dancers' movements with varied patterns of sound and light. While working with the American Negro Ballet, the inventor fell in love with the young prima ballerina Lavinia Williams. His eventual marriage to the African-American dancer caused shock and disapproval in his social circles, but the ostracized couple remained together.
Theremin returned to the Soviet Union in 1938. At the time, the circumstances of his return were unclear, with some claiming that he was simply homesick and others believing that he had been kidnapped by Soviet officials. His wife Lavinia was always certain the latter was true, and many years later it became known that Theremin had indeed been seized by Soviet KGB agents and made to return to his native land. Shortly after he returned, he was at Butyrka prison and later sent to work in the gold mines in Kolyma. Although rumors of his execution were widely circulated, Theremin was in fact put to work in a sharashka, together with Tupolev, Korolev and other well-known scientists and engineers on several tasks. He was rehabilitated in 1956.
Some have suggested that he designed the first "bug" or covert listening device but this is not exactly the case. Theremin's bug was the first to use inducted energy from radio waves of one frequency to transmit an audio signal on another. This made the device difficult to detect since it did not radiate any signal unless it was actively being powered and listened to remotely. This feature also endowed it with (potentially) unlimited operational life. "The Thing", as it was called, was very simple by today's standards, having only a capacitive membrane (a condenser microphone) connected to an antenna. Thus the impedance seen by the quarter-wavelength antenna was altered by sound, and the reflections of the 330 MHz signal impinging on the device were modulated, allowing the audio to be detected. A bug of this nature was embedded in a wooden plaque and presented to the American ambassador in Moscow by Russian schoolchildren where it hung in his office until detected by a professional bug sweeper. 
Theremin invented the first motion detector for automated doors and worked on an early burglar alarm.
In the 1970s, Léon Theremin began training his nine-year-old niece Lydia Kavina on the theremin. Kavina was to be Theremin's last protégé. Today, Kavina is considered the one of the most advanced and famous thereminists in the world.
In 1991, Léon Theremin returned to the United States, where he was reunited with Clara Rockmore who performed a number of concerts at this time. He returned to Russia and died in Moscow in 1993 at the age of 97.
Léon Theremin is the subject of the documentary film, Theremin – An Electronic Odyssey, written, directed, and produced by Steven M. Martin. The documentary was a winner at the Sundance Film Festival in 1994. The film features legendary thereminists Clara Rockmore and Lydia Kavina as well as electronic instrument pioneer Robert Moog, founder of The Beach Boys Brian Wilson, and Theremin himself.
- Theremin – Ether Music and Espionage by Albert Glinsky with a foreword by Robert Moog. University of Illinois Press, 2000.
- Theremin – An Electronic Odyssey, written, directed and produced by Steven M. Martin. Orion/MGM, 1994
- Lev Sergeivitch Termen: The Inventor of the theremin
- An Interview with Léon Theremin
- Online bibliography about both the man and the instrument
- An encounter with Léon Theremin
- History of the theremin from Moog Music
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