Mark Harmon starred as Leroy Jethro Gibbs on NCIS and also served as executive producer of the show. On the new CBS series, NCIS: Origins which explores the early career of Gibbs, Harmon will serve as narrator in addition to executive producer. In other television work, Harmon received an Emmy nomination for Outstanding Guest Actor in a Drama Series for the critically acclaimed The West Wing and for Outstanding Supporting Actor in a Drama Special for Eleanor and Franklin: The White House Years. Other credits include Reasonable Doubts, for which he received two Golden Globe nominations, Chicago Hope, From Earth to the Moon, St. Elsewhere, and Moonlighting.

Leon Carroll, Jr. co-authored the New York Times bestseller Ghosts of Honolulu. He previously served as technical advisor on the hit drama NCIS for twenty-one seasons and is currently working on the new show NCIS: Origins. Previously, he was a commissioned officer in the United States Marine Corps, attaining the rank of Major. Leon then began a twenty-year career as a Special Agent with the Naval Criminal Investigative Service (NCIS). He served in seven different locations, including tours as a Special Agent Afloat on the USS Ranger (CV-61) and as the Special Agent in Charge of NCIS offices in the Republic of Panama and the Pacific Northwest.