Easily one of the most brilliant men to have ever dabbled in the physical realms. His ideas were revolutionary, especially for his time. It is rather a shame that the governments of the world pushed him away and confiscated all of his research. Outside of the "death ray", I really think his work could have contributed even more than it already has to modern day physics. My only qualm would be the death ray. While it may end all war, if a single person got their hands on one or learned to make one, it could very well be the end of life on earth, or, slightly less dramatic, a mass killing in a country of his choosing.
Brilliant, brilliant man. Kinda nuts.