Lee de Forest, American engineer and academic, invented the Audion tube (died 1961)

Lee de Forest was an American inventor, electrical engineer and an early pioneer in electronics of fundamental importance. He invented the first practical electronic amplifier, the three-element "Audion" triode vacuum tube in 1908. This helped start the Electronic Age, and enabled the development of the electronic oscillator. These made radio broadcasting and long distance telephone lines possible, and led to the development of talking motion pictures, among countless other applications.

The Audion was an electronic detecting or amplifying vacuum tube invented by American electrical engineer Lee de Forest as a diode in 1906. Improved, it was patented as the first triode in 1908, consisting of an evacuated glass tube containing three electrodes: a heated filament, a grid, and a plate. It is important in the history of technology because it was the first widely used electronic device that could amplify. A low power signal at the grid could control much more power in the plate circuit.