James Watt (1736–1819) was a Scottish inventor and engineer whose improved steam engine helped power the Industrial Revolution. So central was he to the age of machines that the world's unit of power now carries his name.
Watt didn't invent the steam engine, but he made it vastly more efficient by adding a separate
chamber to condense the steam, so the engine stopped wasting energy reheating itself. That leap in
Watt had a marketing problem: how do you sell an engine to people who only know horses? So he invented "horsepower," measuring how much a strong pony could haul and rating his machines against it. It was clever salesmanship dressed as science — and it stuck so well that we still quote car engines in horsepower today. Fittingly, one horsepower turns out to be about 746 of the watts later named in his honour, so his old advertising trick and his modern unit are neatly linked forever.