James Watt was born in 1736 and died in 1819. James Watt's great claim to fame is that he greatly improved on the steam engine thus paving the way for their use in factories, mills, mines etc.
The invention of the steam engine is credited to Thomas Savery and Thomas Newcomen. Their steam engines were used at their time to pump out water from coal mines. However, their machines were slow and less than reliable.
Watt was born in Greenock, Scotland and he started his professional life as a mathematical-instrumental maker. He became interested in steam engines and determined that he could improve on Newcomen's. By 1769, he had built an improved version of the steam engine using a separate condensing chamber which allowed the machine to continue working all the time - something that Newcomen's engine could not do. Watt also insulated his cylinder to maintain the high temperatures that were needed for maximum efficiency.
Watt could not have succeeded at this stage of his new career without money. This he got from John Roebuck - also a British inventor. In 1775, Roebuck was replaced by Matthew Boulton who owned the Soho Engineering Works in Birmingham. It was at this time that Watt started to manufacture steam engines for sale. Between 1775 and 1800, Watt was involved in further research on steam engines and he continued making important changes to his machines. He produced a steam pressure gauge to record pressure in a cylinder and a rotary engine which could drive various forms of machinery.
In 1800, Watt retired from work to devote his life to research. Though he did not invent the steam engine, he fundamentally changed what Newcomen and Savery had invented and the impact of his new versions of the steam engine on the Industrial Revolution cannot be understated. In recognition of the importance of his work, the electrical unit, the watt, was named after him and in his honour.