Mark Greaney has a degree in international relations and political science. With Tom Clancy he is the coauthor of Locked On, Threat Vector, Command Authority, and Support and Defend. He is also the author of the bestselling Gray Man series. In his research for these novels, he traveled to more than fifteen countries and trained alongside military and law enforcement in the use of firearms, battlefield medicine, and close-range combat tactics. He lives in Memphis, Tennessee.