The theremin was invented in 1921 by Leon Theremin (nee Lev Termen). It is one of the most important musical instruments of the twentieth century because it is the first electronic intsrument. Leon Theremin first came up with the idea for the theremin when in high school. He noticed depending on how close a person stands to a Tesla coil, the coil hums in different pitches. After its inveiling in 1921, Theremin toured his instrument around Russia, sparking the curiosity of almost everybody who saw it.
The theremin made its way to America in 1928, where it gained more popularity. In 1929, RCA bought the rights to manufacture the instrument. Leon Theremin stayed in America, where he met Clara Rockmore, the theremin's first virtuoso. Theremin worked on many variations of his original instrument including the Terpsitone (controlled by the entire body), an electric cello, and a theremin controlled only by the eyes.
In 1954 Robert Moog (famous for his synthesizers of the same name) started production of the theremin. His company, Big Briar Inc., still produces them today. It also produces kits for those who wish to build their own theremin. The popularity of the theremin started to rise again and it was included in several movies (The Day the Earth Stood Still, Spellbound, and Lost Weekend). The Beach Boys and Led Zeppelin both used it in their hit songs "Good Vibrations" and "Whole Lotta Love," respectively.
Leon Theremin died in 1993, but his interesting instrument still has a cult following today. His original theremin's tubes have been replaced by transistors and soon infra-red controllers. Although it may not be the most popular instrument today, it certainly is one of the most interesting.