The Unknown Known, is a 2013 American documentary film about the political career of former U.S. Secretary of Defense and congressman Donald Rumsfeld, an American retired politician and businessman, heserved as the 13th Secretary of Defense from 1975 to 1977 under which President?  
Donald Rumsfeld:  Rumsfeld served as the 13th Secretary of Defense from 1975 to 1977 under President Gerald Ford, and as the 21st Secretary of Defense from 2001 to 2006 under President George W. Bush.
i don't know