The name James Watt (1736-1819) goes hand in hand with the invention of the steam engine. Nevertheless, a certain type of the steam power machine was already developed before James Watt. This machine was used in coal-mines to pump up soil water.

The Scottish inventor James Watt improved the steam engine a lot. In his
machines the steam was condensed outside the cylinder and he altered the
back and forth movement into a rotating movement.

By this innovation steam engines could be used in industries (around
1785). Here you see a model of Watt's steam engine. By the way, James Watt was the first to use the term "horsepower" to indicate the capacity of a machine.