This letter, signed by Einstein, paved the way for the atom bomb. Except it's not Einstein's letter. It was actually written by a man named Leó Szilárd.
Leó Szilárd was a great physicist and accent mark enthusiast. While some physicists thought about the philosophical implications of the fact that atoms weren't as indivisible as previously thought, he went straight for the practical. He patented the idea of the nuclear reactor, which has made him more controversial than scientists, like Einstein, who dealt in the airy realms of time and space. (Click the image below to enlarge the letter.)
Arguably, though, he was the most brilliant futurist of his generation. Not only did he see the future coming, he lent a hand in making it happen. On August 2, 1939, with war on the horizon, Albert Einstein sent a letter to President Franklin Roosevelt. It spelled out the possibility of a bomb being made due to the fission of atoms starting a chain reaction. It didn't actually come from Einstein. Szilárd wrote the whole thing and prevailed upon Einstein to send it off, knowing he didn't have the juice to get the president interested.
I enjoy the fact that he mentions himself several times in the third person - either because it was necessary to give a full picture of the research, or to give himself some credit, or to ensure himself a place at the table if the letter spurred government action. Roosevelt took the letter seriously, and replied - to Einstein - assuring him that he would assemble an investigative board to look into the possibility. The rest is famous, and infamous, history.