Colin O'Brien is a normal guy.
I say this because that is what he says he is, or at least what he was at the time the trouble started. He says he was "a normal guy having a normal day at a normal Starbucks, enjoying a normal cup of coffee". That's when a woman in her late 30s or so approachs him and asks for a meeting. When he declines, she asks how much he would charge for one and, humoring her, he quoted $10k. She handed it to him. That got his attention. So he goes to the meeting and finds he has been mistaken for a highly dangerous and successful assassin and he is offered $1m to kill someone. Again using his own words, "Being offered $1,000,000 to kill a man can really skew your prerogatives in life".
Things get interesting from that point.