Napoleon Alphonseau Chagnon (August 27, 1938 – September 21, 2019) was an American anthropologist, professor of anthropology at the University of Missouri in Columbia and member of the National Academy of Sciences. Chagnon was known for his long-term ethnographic field work among the Yanomamö, a society of indigenous tribal Amazonians, in which he used an evolutionary approach to understand social behavior in terms of genetic relatedness. His work centered on the analysis of violence among tribal peoples, and, using socio-biological analyses, he advanced the argument that violence among the Yanomami is fueled by an evolutionary process in which successful warriors have more offspring. His 1967 ethnography Yanomamö: The Fierce People became a bestseller and is frequently assigned in introductory anthropology courses.
Admirers described him as a pioneer of scientific anthropology. Chagnon was called the "most controversial anthropologist" in the United States in a New York Times Magazine profile preceding the publication of Chagnon's most recent book, Noble Savages: My Life Among Two Dangerous Tribes—the Yanomamö and the Anthropologists, a scientific memoir.