Rudolph Joseph Rummel (October 21, 1932 – March 2, 2014) was an American political scientist, a statistician and professor at Indiana University, Yale University, and University of Hawaiʻi at Mānoa. He spent his career studying data on collective violence and war with a view toward helping their resolution or elimination. Contrasting genocide, Rummel coined the term democide for murder by government, such as the genocide of indigenous peoples and colonialism, Nazi Germany, the Stalinist purges, Mao Zedong's Cultural Revolution, and other authoritarian, totalitarian, or undemocratic regimes, coming to the conclusion that democratic regimes result in the least democides.

Rummel estimated that a total of 212 million people were killed by all governments during the 20th century, of which 148 million were killed by Communist governments from 1917 to 1987. To give some perspective on these numbers, Rummel stated that all domestic and foreign wars during the 20th century killed in combat around 41 million. His figures for Communist governments have been criticized for the methodology which he used to arrive at them, and they have also been criticized for being higher than the figures which have been given by most scholars. In his last book, Rummel increased his estimate to over 272 million innocent, non-combatant civilians who were murdered by their own governments during the 20th century. Rummel stated that his 272 million death estimate was his lower, more prudent figure, stating that it "could be over 400,000,000." Rummel came to the conclusion that a democracy is the form of government which is least likely to kill its citizens because democracies do not tend to wage wars against each other. This latest view is a concept, which was further developed by Rummel, known as the democratic peace theory.

Rummel was the author of twenty-four scholarly books, and he published his major results between 1975 and 1981 in Understanding Conflict and War (1975). He spent the next fifteen years refining the underlying theory and testing it empirically on new data, against the empirical results of others, and on case studies. He summed up his research in Power Kills (1997). His other works include Lethal Politics: Soviet Genocides and Mass Murders 1917–1987 (1990), China's Bloody Century: Genocide and Mass Murder Since 1900 (1991), Democide: Nazi Genocide and Mass Murder (1992), Death by Government: Genocide and Mass Murder Since 1900 (1994), and Statistics of Democide (1997). Extracts, figures, and tables from the books, including his sources and details regarding the calculations, are available online on his website. Rummel also authored Applied Factor Analysis (1970) and Understanding Correlation (1976).

Rummel was born in 1932 in Cleveland, Ohio, to a family of German descent. A child of the Great Depression and World War II, he attended local public schools. Rummel received his Bachelor of Arts and Master of Arts from the University of Hawaiʻi in 1959 and 1961, respectively, and his PhD in political science from Northwestern University in 1963.

Rummel died on March 2, 2014, aged 81. He is survived by two daughters and one sister.

Rummel began his teaching career at Indiana University. In 1964, Rummel moved to Yale University, and in 1966 returned to the University of Hawaiʻi at Mānoa, where he taught for the rest of his active career. In 1995, Rummel retired and became professor emeritus of political science. His research was supported by grants from the National Science Foundation, DARPA, and the United States Peace Research Institute. In addition to his books, Rummel was the author of more than 100 professional articles.

Rummel was a member of the advisory council of the Victims of Communism Memorial Foundation.

Rummel coined democide, which he defined as "the murder of any person or people by a government, including genocide, politicide, and mass murder." Rummel further stated to "use the civil definition of murder, where someone can be guilty of murder if they are responsible in a reckless and wanton way for the loss of life, as in incarcerating people in camps where they may soon die of malnutrition, unattended disease, and forced labor, or deporting them into wastelands where they may die rapidly from exposure and disease."