Whose invention was the first successful practical steam engine?

Although earlier steam engines existed, James Watt’s improvements made the machine practical on a much wider scale. Working in the 1760s and 1770s, Watt added a separate condenser that greatly improved efficiency. With business partner Matthew Boulton, he helped power factories, mines, and transport. The steam engine became a key technology of the Industrial Revolution. Watt’s name later became the unit of power in science and engineering.