Hawk, Cowboy, and Liz are agents of the American President.
Diego Black Hawk, Hawk to everyone, is a veteran of two tours in Southeast Asia, having been a part of missions in Vietnam, Laos, Cambodia, and Thailand. As we are told when we first meet him, "they had all taken their toll on his mind and body". This is shown as we watch him have a particularly nasty nightmare in which he relived a mission to kill a traitor. "It was one of the many recurring nightmares that frequented his life when he slept. They were all different, but starkly exact in every detail of the way they happened"
The fact that Hawk is safely in his Rocky Mountain home when the bad dreams hit him does nothing to alleviate the trauma. And unfortunately for Hawk, the timeframe of these issues is the early 70s, back before the mental struggles of PTSD had such a clinical designation. The memories might ruin his night rests but they do not slow down his ability to carry out required violence, as the two would be Mexican assailants in our initial meeting of Hawk learn the hard way.
Hawk is 6' tall and still very much in terrific shape, which he keeps by running every day the roads were not blocked by feet of snow. He has "straight black hair, cool black eyes, and a chiseled, linear jaw that women found eye-catching".
Cowboy's real name is Juan Luis Diaz Villalobos. He is a bit younger than Hawk, his closest friend whom he met while in the Service and who credited with helping Cowboy make it back home alive. Hailing from El Paso, Cowboy returned to the ranch that his father owned outside the city when his tours ended and it is there that he is living when Hawk reenters his life needed help from his own friend.
Liz is Elizabeth Shillings, daughter of a prominent U.S. Senator. When we first meet her, she is a prisoner of a particularly nasty drug cartel leader out of Quintana Roo, Mexico, in need of being rescued because her anti-drug activities had earned his wrath. A former drug user herself, she had a bad attitude towards those who trade in the misery. While she did need assistance getting free, she shows Hawk and Cowboy she is one very capable individual and it is not long before she becomes part of this unofficial team.
The two men will be asked by the President to handle a matter off-book and when they pull out that nearly impossible task, that Chief Executive will not hesitate to call upon them again, this time with Liz as their teammate.