Nikola Tesla arrived in New York in 1884 with little more than a letter of introduction to Thomas Edison and a handful of cents in his pocket, having already designed much of an alternating current motor system in his head during his engineering studies in Europe, at a time when Edison's rival direct current system dominated American electrical thinking.
He briefly worked for Edison's company, but the two clashed sharply over which electrical system was actually better for large-scale power distribution, a disagreement that escalated into a public rivalry known as the 'War of Currents,' with Edison publicly staging demonstrations to discredit alternating current as dangerous.
Tesla left to develop his AC system independently, eventually partnering with industrialist George Westinghouse, and in 1893 the pair won the contract to light the World's Columbian Exposition in Chicago and later to harness Niagara Falls for hydroelectric power — practical, large-scale proof that alternating current, not Edison's direct current, was the more efficient system for delivering electricity across long distances.
Despite this technical victory, Tesla struggled financially for much of his later life, having signed away lucrative royalty rights years earlier to help Westinghouse's company survive a financial crisis, and he died in 1943 with comparatively little money, even as the AC power system he had championed became the electrical standard used across the world.