Nikola Tesla was a genius polymath, inventor and a mechanical and electrical engineer. He is frequently cited as one of the most important contributors to the birth of commercial electricity, a man who ""shed light over the face of Earth,"" and is best known for his many revolutionary developments in the field of electricity and magnetism in the late 19th and early 20th centuries. Tesla's patents and theoretical work formed the basis of modern alternating current (AC) electric power systems, including the polyphase power distribution systems and the AC motor, with which he helped usher in the Second Industrial Revolution. Born an ethnic Serb in the village of Smiljan, Vojna Krajina, in the territory of today's Croatia, he was a subject of the Austrian Empire by birth and later became an American citizen. After his demonstration of wireless communication (radio) in 1894 and after being the victor in the ""War of Currents"", he was widely respected as one of the greatest electrical engineers who worked in America. Much of his early work pioneered modern electrical engineering and many of his discoveries were of groundbreaking importance. During this period, in the United States, Tesla's fame rivaled that of any other inventor or scientist in history or popular culture, but due to his eccentric personality and his seemingly unbelievable and sometimes bizarre claims about possible scientific and technological developments, Tesla was ultimately ostracized and regarded as a mad scientist. Never having put much focus on his finances, Tesla died impoverished at the age of 86.