Nikola Tesla (Serbian Cyrillic: Никола Тесла) (10 July 1856 – 7 January 1943) was an inventor, physicist, mechanical an electrical engineer. Born in Smiljan, Croatian Krajina, Austrian Empire, he was an ethnic Serb subject of the Austrian Empire and later became an American citizen. Tesla is best known for many revolutionary contributions in the field of electricity and magnetism in the late 19th and early 20th century. Tesla's patents and theoretical work formed the basis of modern alternating current electric power (AC) systems, including the polyphase power distribution systems and the AC motor, with which he helped usher in the Second Industrial Revolution. Contemporary biographers of Tesla have deemed him The Father of Physics and the man who invented the twentieth century and "the patron saint of modern electricity".