When I was younger I asked for, and got, a book on Nikola Tesla.  I only wanted it cause the description of the book mentioned a death ray, an earthquake machine, and free electricity from the air.  I tried making sense of everything in the book but I was young and didn't understand much of the technical details.  

As I got older I, and online, I started researching Tesla and found that he did indeed invent many many things that where revolutionary.  He almost leveled a city block in NY with his earthquake machine.  He had radar during WW1.  He built the Wardenclyffe Tower in Long Island, NY as a prototype for wireless electricity.  It would have revolutionized our way of life, and perhaps even prevented things like global climate change.

So, you might be wondering, what happened?  Here's a really good summary of Tesla's work and why it didn't catch on.  Hint: Thomas Edison was a douche.