John Learie Estrada (born September 27, 1955) is the former United States Ambassador to Trinidad and Tobago and a former United States Marine who served as the 15th Sergeant Major of the Marine Corps from 2003 to 2007. Estrada stepped down from that post on April 25, 2007, turning over the billet to the next sergeant major, Carlton Kent. Estrada then retired from the military in June 2007, after over 33 years of service. He has also worked as a senior manager for Lockheed Martin Training Solutions from 2008 onward.