Jacob Snow is an agent with the CIA.
When we are introduced to him in the first recorded adventure, he is not having a particularly good day thanks to being tied to a chair and receiving painful blows from a fist. That fist belonged to a member of an Al Qaeda splinter group and the chair was in a house in the suburbs of Damascus. When physical beating did not get them the info they wanted and the suggestions of severing fingers is broached as the next stage in the torture, that is when Snow felt it time to make use of an unusual skill taught him by his parents as a child - he used a special maneuver to dislocate one shoulder, pull that arm from of the restraints, pop it back into place, and then repeat the process for the other side. After that painful procedure, subduing the three torturers seemed almost anticlimactic.
That trick, as mentioned, had been taught him when he was little. It would have been fascinating to learn more about his upbringing but (as of this writing) we know very little except the tantalizing: "Some kids dreamed of running away and joining the circus. Jacob didn't have to. He grew up in the circus".
The part we do get told a good deal about concerning Snow before he went to work for the Agency is not as fun to imagine. He was a proud member of the elite U.S. Army Rangers, serving yet another tour in Afghanistan, when the horror happened. Weeks of constant stress and tension and danger led up to a terrible incident in which the squad team he was in "snapped". Snow watched his fellow soldiers retaliate an ambush by taking their anger out on villagers; rather than watch more innocents die, Snow had fought his own side.
"That's when Jacob's mind broke", is what we are told. That followed by months of his living in the mountain region on his own until a CIA agent named Peters, sent to eliminate him, decided to save him instead. A considerable amount of time later, Snow went to work for the Agency.
The name Peters will play an important role in Snow's life beyond the man who saved him and gave him a new life. His grown daughter, Dr. Jana Peters, a noted archaeologist, will somewhat unwillingly get thrust into Snow's sphere and whether they want it or not, the two will become enmeshed. Dr. Peters may not have Snow's fighting skills or inclinations, but it would be a bad mistake to discount her in any way.