Leo Szilard. Had the idea for fission chain reaction, realized what would happen if Hitler got hold of it, and kept his mouth shut... while browbeating the skeptical Fermi into starting the Manhattan Project, and ghostwriting Einstein's letter to Roosevelt.
Right up there with Norman Borlaug and Stanislav Petrov on the list of people you've never heard of because CNN is too busy covering Michael Jackson.
I'll stick with Borlaug. I know singing his praise has become slightly cliched on this forum, but he very objectively deserves it. He's done more for humanity than anyone since whoever it was that discovered how to make fire.
So happy to see him mentioned - I recently read a collection of his short stories (The Voice of the Dolphins) and highly recommend it. His writing is somewhat dry, but really gives you a perspective on how people thought during the cold war era.
Right up there with Norman Borlaug and Stanislav Petrov on the list of people you've never heard of because CNN is too busy covering Michael Jackson.