Robert Fulton

Fulton caught the steam bug at twelve, visiting a Pennsylvania delegate who'd seen Watt's engine in England and couldn't stop talking about it. By 1800 he was in France building Nautilus for Napoleon — the first practical submarine — and sketching out naval torpedoes for the British Navy. But the legacy locked in 1807: the North River Steamboat carried passengers 300 nautical miles on the Hudson, proved the economics worked, and turned every major American river into a different kind of artery. He died in 1815, eight years after the trip that changed the map.