James Watt was an instrument maker and engineer whose genius fueled the Industrial Revolution. While repairing a Newcomen steam engine, he realized that it wasted vast amounts of energy by cooling and reheating the cylinder. His breakthrough was the 'separate condenser,' which allowed the cylinder to stay hot while steam was condensed elsewhere, drastically increasing efficiency. Watt also developed the 'sun and planet' gear to convert linear motion into rotary motion, allowing steam engines to power factory machinery. He coined the term 'horsepower' to compare his engines' power to that of draft horses. The SI unit of power, the 'Watt,' is named in his honor.