The Osage Indian murders were a series of murders of Osage in Osage County, Oklahoma, during the 1910s–1930s. Newspapers described the increasing number of unsolved murders and deaths among young adults as the "Reign of Terror". Most took place from 1921 to 1926. Some sixty or more wealthy, full-blood Osage persons were reported killed from 1918 to 1931. Newer investigations indicate that other suspicious deaths during this time could have been misreported or covered-up murders, including those of individuals who were heirs to future fortunes. Further research has shown that the death toll may have been in the hundreds.

John Joseph Mathews became one of the Osage Nation's most important spokespeople and writers of the mid-20th century, and served on the Osage Tribal Council from 1934 to 1942. Mathews was born into an influential Osage family, the son of William Shirley Mathews an Osage Nation tribal councilor. He studied at the University of Oklahoma, Oxford University, and the University of Geneva and served as a pilot during World War I.