Thomas Newcomen invented the first practical steam-powered engine in 1712 to pump water out of coal and tin mines in Cornwall.
James Watt developed an improved version of Newcomen's engine in 1769 which used 75% less coal, and which was therefore cheaper to run.
After entering into a partnership with a Birmingham man called Matthew Boulton, he then modified it further in 1783 to provide a rotary (turning) motion for driving factory machinery.
As it was so reliable and didn't need to be sited near a river to work (unlike older waterwheels), the Boulton and Watt steam engine soon became the main source of energy used in industries, with many people saying that it fuelled the start of the Industrial Revolution.
Factories could now produce large amounts of goods in numbers unimaginable in previous periods.
The textile manufacturer Sir Richard Arkwright, for example, used it in many of his cotton mills.