Nikola Tesla was primarily an electrical engineer. He is responsible for the electrical system we use today. Tesla made the generators and transformers necessary to produce electricity and transmit it over significant distance. He also invented radio. At the time he called it a "wireless"; he at first in 1892, invented a means of wirelessly controlling devices, by doing so also invented the first robotic machines. He made prototypes of wireless-controlled boats. He tried to sell his idea to have a wireless armada, complete with plans, for what would later be know as torpedoes. He later came up with the idea to make a global system using wireless communications. He initiated the invention of X-rays, radar, and a blade less turbine, among other inventions. Mostly, he was known for pioneering modern electricity - most especially, the general use of alternating current.
Nevertheless, as many others throughout history, many inventions were so far ahead of his time few understood what he was doing. This made it hard to find investors for certain projects. The lack of investors and the fact that he gave away what would have been billions today in rights to his patents, meant that instead of being possibly the richest man in history, he died in debt and not completing many of his projects. Some of his inventions mistakenly get credited to others.