Peter Black is an agent with the CIA.
He is, more accurately, an assassin with the Agency, a very dangerous killer operating under the codename of Azrael, one of the names for the Angel of Death.
And even more accurately, when we meet him, the verb is 'was', not 'is'. He is still very much a killer though now he is doing so for considerable money in the private sector because he had a few years before decidedly separated from the CIA and both parties were happier as a result. The CIA did not want to acknowledge he still existed. Until, of course, they need him again.
In flashbacks we watch, a couple decades before, two squad cars respond to a call at St. Joseph's Orphanage, the results of their intervention being four injured and annoyed policemen. The cause was a resident of that facility, an eleven-year-old boy who had decided he had had enough of the 'care' being given by its head man, the now late Father Collins. It was after the violent scuffle that a woman whose ID said she was an agent with the FBI arrived and she presented the paperwork place the preteen into her custody.
Within the hour she and the boy, suffering without complaint from a broken collarbone, enjoyed a breakfast at a Denny's before boarding a plane headed to the boy's new home, training facility in Alaska. It is in that northernmost state that Peter Black learns the art and science of killing and becomes the even more hardened individual whose killing style would earn him the Azrael codename.
Black has an amazing ability to observe and quickly assimilate. Coupled with his eidetic memory, he can recall virtually everything he has seen and heard, every document he has even briefly scanned. It is considered a major asset for someone in his line of work but it is also pointed out that he was "cursed to remember everything". As for himself, he is not what people would consider that memorable. To look at him would not spark thoughts of danger, described as a "5'10" mouse". And his skill with changing his facial appearance makes even accurate accounts useless as he would frequently change the way he looked.
Black is a very serious man virtually all the time; at one point when a fairly recent colleague accuses him of 'kidding' him, Black asks, "In the time you've known me, have I ever told a joke?" The answer was no.