The modern synthesizers evolution began in 1919, when a Russian physicist named Lev Termen (also known as Lon Theremin) invented one of the first electronic musical instruments the Theremin. It was a simple oscillator that was played by moving the performers hand in the vicinity of the instruments antenna. An outstanding example of the Theremins use can be heard on the Beach Boys iconic smash hit Good Vibrations.
In the late 1930s, French musician Georges Jenny invented what he called the Ondioline, a monophonic electronic keyboard capable of generating a wide range of sounds. The keyboard even allowed the player to produce natural-sounding vibrato by depressing a key and using side-to-side finger movements. You can hear the Ondioline on Del Shannons Runaway.