William Mark Felt , Sr. ( August 17 , 1913 -- December 18 , 2008 ) was a Federal Bureau of Investigation ( FBI ) special agent who retired as the Bureau 's Deputy Director in 1973 .
William Mark Felt , Sr. ( August 17 , 1913 -- December 18 , 2008 ) or W. Mark Felt was an agent of the Federal Bureau of Investigation ( FBI ) , who retired as the Bureau 's Associate Director in 1973 .