As with many myths about famous inventors, the story of Tesla tends to overlook the contributions of those who came before him. In 1856 when Tesla was born, AC, or alternating-current, power had already been in existence for more than two decades, and by the time Tesla was a young man, AC transformers and experimental power grids were already up and running in Europe. Where Tesla did play a role in AC power was in making it more practical: at the time, electric motors could only run on DC, or direct current. AC had to be converted to DC power to run an electric motor, which was inefficient. Tesla built a working prototype of an electric induction motor that worked on AC power, although that happened two years after inventor Galileo Ferraris built the same thing.
Likewise, Tesla didn't invent radio. Along with Guglielmo Marconi, Tesla developed a device that enabled wireless communication in 1896, which eventually won Marconi the Nobel Prize. But that was after Russian physicist Alexander Popov demonstrated his own radio receiver in 1895, and—again, like most inventions—both devices were based on the the developments of many, many other scientists that came before. The same goes for radar: along with Marconi, Heinrich Hertz and Christian Hülsmeyer made large contributions to the technology before Tesla came on the scene. Both of these inventions are why many say that without Tesla, we wouldn't have Wi-Fi, which is true. But without scientists like Michael Faraday, Tesla wouldn't have had AC power. Technology is a chicken-and-egg problem, and it's rare that one man is responsible for a single invention.