Hermann Joseph Muller (or H. J. Muller) (December 21, 1890 – April 5, 1967) was an American geneticist, educator, and Nobel laureate best known for his work on the physiological and genetic effects of radiation (X-ray mutagenesis) as well as his outspoken political beliefs. Muller frequently warned of the long-term dangers of radioactive fallout from nuclear war and nuclear testing, helping to raise public awareness in this area.