The AGA cooker was invented in 1922 by Swedish physicist Gustaf Dalén. Constructed of cast iron, it was a technological advancement at the time, using heat storage from slow-burning coal to power its ovens and cooktop. There was never a fire to make or tend—the AGA was always ready to use. The AGA is still produced today but criticized for its energy inefficiency. A modern range uses less than 3 percent of the fuel an AGA requires.