Charles Hall was an economist who studied the energy system and its effects on the economy. He believed that energy from natural resources like oil, gas, and coal was very important, and that a better understanding of how energy created wealth was needed in order to improve society. He developed a way to measure how different types of energy were used in the economy, and how changes in the energy system would affect economic growth. He argued that when countries and companies stopped using easily available energy like oil and gas, it had long-term effects on their economic health and development.