America's first steamboat was built by who?

The first steam-powered boat built in America is credited to William Henry of Lancaster Pennsylvania (1763). However, Henry's first, and subsequent boats proved prone to sinking.

The creator of the first commercially viable steamboat in America was Robert Fulton. Fulton had visited William Henry and seen, firsthand, his early efforts. Fulton improved the efficiency of the steam engine and the seaworthiness of the boat and launched a Golden Age of trade and travel with his first commercial steamboat in 1807.

Fulton also designed the first working submarine.