Contrary to popular belief, James Watt never invented the concept of steam engine.
In fact, the first steam engine was designed back in 1655 by Edward Somerset, 2.nd Marquess of Worcester. In year 1685, first functional model was built by Denis Papin, and in year 1712, 24 years before James Watt was born, Thomas Newcomen from Tipton managed to build the first working prototype.
James Watt was never credited for inventing the first steam engine, but rather for introducing a separate steam condenser, which avoided the unwanted waste of energy and greatly improved the efficiency and power of steam engines. In addition, he also designed the first steam engine capable of rotary motion.
Without his improvements, the First Industrial Revolution wouldn’t probably take place, as previous steam engines wasted very large amounts of energy by cyclically cooling and re-heating the same cylinder, and could be used only for water pumping.