Mark "Oz" Geist is a member of the Annex Security Team that fought the Battle of Benghazi, Libya, from September 11 to September 12, 2012. A Colorado native, Mr. Geist joined the United States Marine Corps in 1984.

After serving 12 years in the United States Marine Corps, Mr. Geist became a Deputy Sheriff in Teller County, Colorado. In that role, he was assigned as liaison with the Vice Narcotics and Intelligence Unit in Colorado Springs, Colorado, as well as an Investigator for Crimes against Children.

In 2004, Mr. Geist began doing contract security work in Iraq. He worked for Triple Canopy, providing Personal Security Details for Department of State personnel in Baquba, Iraq.

Mr. Geist finished his career as a security contractor in Benghazi, Libya, where he was credited with helping to save the lives of more than 25 Americans. Mr. Geist is still recovering from the injuries he sustained in the battle. He is a co-author of the bestselling book "13 Hours: The Inside Account of What Really Happened in Benghazi."