Hans Albrecht Bethe was a German and American nuclear physicist. He was also one of the 20th century's most important theoretical physicists. He helped develop the discipline of quantum physics. During his 60+ year career, Bethe published over 300 scientific papers. For most of that career, he taught at Cornell University. In World War II, he helped the United States develop the atom bomb -- and then spent much of the rest of his life trying to halt nuclear proliferation. During his work with the Manhattan Project, he determined the critical mass of the bombs. As a scientist, he was best known for calculating and determining how stars produce light, and he even won a Nobel Prize for this achievement. He also advised Presidents from Truman to Clinton on scientific matters. Although he retired from teaching in 1975 he continued with his other pursuits practically until his death. As a lecturer, he had taught generations of physicists in many fields including particle, solid state, nuclear and astrophysics. He was calling for a complete ban on nuclear tests by the 1990s. He also continued writing scientific papers. Towards the end of his life, he was researching and writing about the deaths of stars