The theremin is named after Leon Theremin, who invented it in 1920. Here he is, demonstrating:
A more recent performance:
This is Clara Rockmore playing “The Swan” from Camille Saint-Saëns’s “The Carnival of the Animals”, a piece that was also beautifully choreographed by Mikhail Fokin as “The Dying Swan”, first danced by Anna Pavlova:
And this is Zaz, from Tours, France, playing the instrument in Moscow: