Matt Thorn is an agent with S.O.G.
By that I mean he is a black-ops specialist attached to the Special Operations Group, described as an ultra-secret program meant to combat devastating criminal and terrorist threats, but inside and outside North Ameria. There is historically been a S.O.G. as part of the CIA and this may well be the same but I have no evidence of it.
A good amount of information on his backstory is available.
"A child of the streets, after escaping from an abusive foster home, Thorn had witnessed unspeakable evil and suffering by the time he was twelve years old. He had grown up wild and mean - incorrigible, they called it - with his father in prison and his mother dead at twenty-two from cancer. He had learned to survive on his wits and by honing his fighting skills in back-alley brawls and junk-yard knife fights. He had fallen into the bloody world of gang violence, sinking deeper and deeper, making all the wrong choices - until the day he had found the courage to walk away from thug life and enlist in the U.S. Army, after 9/11.
"His decision had been fueled by patriotism, absolutely. But it was also based on a clear insight. His life was constant struggle, constant warfare - so he would make warfare his profession. He was fated to be a warrior, to spill the blood of those who sought to brutalize the innocent.
"From there, he had braved and withstood the extreme rigors of Special Forces training, graduated with honors. But no amount of training could have prepared him completely for actual combat. He had nearly frozen in a savage battle against Taliban insurgents - red-hot tracers hurtling past his skull, shrapnel flying, comrades screaming and dying around him...his scrotum shrinking, urine staining his pants.
"Now more than a decade later, he was a disciplined professional, a soldier - a Delta Force specialist, focused on defeating the enemy. Defeating evil. His resolve had been sharpened by his time on the streets, by the horror of battle...and by devastating personal tragedy."
We also learn that three years before the start of the recorded adventures, he has lost his wife when she was attacked, raped, and killed. Learning her killers were "gang thugs high on crystal-meth", he went on a rampage and found and "slaughtered them all". At that point he turned himself into to his Delta commander and expected extremely harsh punishment. Instead, he was introduced to S.O.G. and immediately accepted what they were offering.
"So the deal was made. His old identity was erased. Officially, he had been killed in a parachute training accident. His new identity had been carefully designed and his new name was Matt Thorn. He would specialize in solo operations, where a typical Delta Force team might comprise five men. The concept was to maximize stealth and combat flexibility. It was a grim and lonely way to fight...but Thorn had long ince adjusted to it. In some primal way, he thrived on it. He was at his core a lone-wolf hunter and he understood that in certain situations - against certain enemies - one man had a better chance than five. Or ten. Or fifty."
That is what we find him doing - taking the fight to whatever enemy he is aimed at.