Dr. Robert Thurston formerly was a Professor of History at Miami University. He is a Stalin apologist, and wrote a book arguing that Stalin was a bad guy but not responsible for many of the mass killings in the Soviet Union. According to the New York Times, he denies Stalin's role in the purges and also disputes widely-accepted statistics on the amount of people killed under his regime. Thurston also argues that Stalin's subordinates went rogue and killed far more people than Stalin wanted.
Source: http://www.nytimes.com/1996/05/05/books/dark-prince-of-the-kremlin.html https://miamioh.edu/cas/academics/departments/history/about/faculty/faculty-emeriti/thurston/index.html