weapons. Albert Einstein (1879–1955) was a theoretical physicist and philosopher, widely regarded as one of the most influential and best known scientists and intellectuals of all time. A German-Swiss Nobel laureate, Einstein is often regarded as the father of modern physics. His father was Hermann Einstein, a salesman and engineer. His mother was Pauline Einstein (née Koch). The Einsteins were non-observant Jews. In 1933, Einstein was compelled to immigrate to the United States due to the rise to power of the Nazis under Germany's new chancellor, Adolf Hitler. While visiting American universities in April 1933, he learned that the new German government had passed a law barring Jews from holding any official positions, including teaching at universities. A month later, the Nazi book burnings occurred, with Einstein's works being among those burnt, and Nazi propaganda minister Joseph Goebbels proclaimed, "Jewish intellectualism is dead." Einstein also learned that his name was on a list of assassination targets, with a "$5,000 bounty on his head". One German magazine included him in a list of enemies of the German regime with the phrase, "not yet hanged". Leó Szilárd (1898–1964) was a Jewish Hungarian physicist who conceived the nuclear chain reaction in 1933, patented the idea of a nuclear reactor with Enrico Fermi, and in late 1939 wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project that built the atomic bomb. Szilárd left Hungary because of the rising antisemitism under the Horthy regime, which excluded Jewish students from Hungary's universities. Szilárd was directly responsible for the creation of the Manhattan Project. He drafted a confidential letter to Franklin D. Roosevelt explaining the possibility of nuclear weapons, warning of Nazi work on such weapons and encouraging the US development of a program to create them. During August 1939 he approached his old friend and collaborator Albert Einstein and convinced him to sign the letter, lending his fame to the proposal. The Einstein–Szilárd letter resulted in the establishment of research into nuclear fission by the U.S. government and ultimately to the creation of the Manhattan Project; FDR gave the letter to an aide, General Edwin M. "Pa" Watson with the instruction: "Pa, this requires action!" Later, Szilárd relocated to the University of Chicago to continue work on the project. There, along with Fermi, he helped to construct the first "neutronic reactor", a uranium and graphite "atomic pile" in which the first self-sustaining