Potentiometer
The idea of a device that could be used to control the amount of electricity going to a component was thought by many people, but the carbon potentiometer we commonly use today was invented by Thomas Edison in 1872 at the age of 25. He called this device a "coiled resistance wire rheostat". His patent for this device was issued in 1872. Carbon resistors, as said above, are the most commonly used resistors today. They are used in radios to control the volume, in televisions to control picture brightness, contrast, and color response.