Athan Theoharis is a Milwaukee-area American historian and professor of history emeritus at Marquette University. Theoharis earned two bachelor's degrees in political science in 1956 and 1957, a master's degree in 1958 and a Ph.D. in history in 1965, all from the University of Chicago. He has taught at Texas A&M University, Wayne State University, City University of New York, State University of New York at Buffalo, and Marquette University. The scope of his award-winning writings includes 21 books and more than 100 articles on Cold War history, anti-communism in America, civil rights and the politics of government secrecy and surveillance.

In the mid-1970s, at the request of the U.S. Senate, Theoharis began conducting research at presidential libraries. The Church Committee, a U.S. Senate Select Committee created to study governmental operations with respect to intelligence activities, asked Theoharis to conduct research because of his past work exploring FBI wiretapping and the Truman and Eisenhower loyalty and security programs. First without, and later with, qualified security clearances, Theoharis examined presidential records relating to the FBI and White House at the FBI headquarters and the Eisenhower, Kennedy and Johnson presidential libraries. Following this work, Theoharis became a specialist in the history of the FBI, and has testified before Congress on federal wiretapping, Freedom of Information Act (FOIA) law, the FBI charter and Kennedy assassination records legislation.