Jack Abbot is a night-shift ER physician and SWAT tactical doctor in his late 40s with a tall, muscular build and a right-leg prosthesis from his 20-plus years as a military combat medic. He carries a "no-nonsense" tough exterior and an unflappable composure forged by battlefield trauma and the loss of his wife, though he hides a deep empathy beneath a dry, dark sense of humor.