"The Grey Man" is a thriller novel written by Mark Greaney, featuring the character Court Gentry, a skilled assassin known as the Grey Man. The story follows Gentry as he navigates a dangerous world of espionage and betrayal, pursued by various enemies who want him dead. The novel is the first in a series that combines action, suspense, and intricate plotting. Gentry's character is portrayed as a complex anti-hero, making moral choices while trying to survive in a high-stakes environment filled with international intrigue and deadly confrontations.