Edwin Mattison McMillan.

Edwin Mattison McMillan was an American physicist and chemist who made significant contributions to the field of nuclear physics. He discovered the radioactive metal neptunium and codiscovered plutonium, which played a crucial role in the development of nuclear power and nuclear weapons. McMillan also discovered the principle of phase stability, which allowed for advancements in high-energy accelerators and a better understanding of matter. His work on plutonium was instrumental in the Manhattan Project and the development of the atomic bomb. McMillan received numerous awards and honors for his contributions to science and served in various advisory roles. [Extracted from the article]