Short answers, pulled from the story.
James Watt was a Scottish inventor, engineer and chemist, born in Greenock on the 19th of January 1736 and died on the 25th of August 1819. He improved Thomas Newcomen's steam engine by adding a separate condenser, and his other inventions include a letter-copying machine, the sun and planet gear, the parallel motion linkage and a centrifugal governor.
The separate condenser was Watt's key improvement, conceived in May 1765 as he crossed Glasgow Green park. By condensing steam in a separate chamber and keeping the cylinder hot with a steam jacket, it stopped the engine wasting about three-quarters of its thermal energy on reheating, making the engine up to five times as fuel efficient as a Newcomen engine.
The watt is named after James Watt for his contributions to the development of the steam engine, building on his work developing the concept of horsepower. It was adopted by the British Association for the Advancement of Science in 1889 and by the 11th General Conference on Weights and Measures in 1960 as the SI unit of power.
Matthew Boulton owned the Soho Manufactory near Birmingham and acquired Watt's patent rights after John Roebuck went bankrupt. Their firm, Boulton and Watt, began in 1775 and lasted 25 years, and the two men appear together on a Bank of England £50 note announced on the 29th of May 2009.
James Watt died on the 25th of August 1819 at his home, Heathfield Hall near Handsworth in Staffordshire, now part of Birmingham, at the age of 83. He was buried on the 2nd of September in the graveyard of St Mary's Church, Handsworth, and later expansion of the church means his grave is now inside it.
James Watt went to court after infringers such as Edward Bull and the Hornblower brothers built engines using a separate condenser. He first sued Bull in 1793 and won, and a decisive verdict in his favour came when Jonathan Hornblower was tried in 1799. Of the £21,000 owed to Boulton and Watt, only £2,500 had been received by 1795.