Serling was a 23rd century Human male. By the mid-2260s, Serling served in Starfleet as a command division captain in command of the USS Defiant. Serling was regarded as a no-nonsense type of commander who doesn't like to see his personnel deviate from the rules, especially newly assigned crew members. Prior to her taking up her posting aboard the Defiant, Lieutenant Mariah Willoughby sought James T. Kirk's advice about serving under Serling. (TOS - My Brother's Keeper novel: Constitution)