Watt attempted to commercialize his invention, but experienced great financial difficulties until 1775 he entered a partnership with Matthew Boulton. The new firm of Boulton and Watt was eventually highly successful and Watt became a wealthy man. In his retirement, Watt continued to develop new inventions though none were as significant as his steam engine work. He died in 1819 at the age of 83. Watt has been described as one of the most influential figures in human history.
He developed the concept of horsepower and the SI unit of power, the watt, was named after him.