Nikola Tesla was an inventor and a mechanical and 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 often described as the most important scientist and inventor of the modern age, a man who "shed light over the face of Earth". He is best known for many revolutionary contributions 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 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 regarded him as "The Father of Physics", "The man who invented the twentieth century“ and "the patron saint of modern electricity.“