Sean Faint is an agent with The Company.
Being British, that designation does not stand for the CIA as it might in America; it stands for an unnamed, unspoken, and very much unacknowledged agency inside the U.K.'s intelligence community. While its operatives could and did gather valuable information wherever they were sent to trouble-shoot, in truth their main function was considerably more drastic and severe, not to mention permanent.
"The public wouldn't want to know that the company Faint worked for had no name, had no one to answer to either. If Britain was a computer, then The Company was a piece of anti-virus software, attacking any bug that was designated dangerous by the board of ex-military advisors that gave their direct orders to Faint's boss: Smith."
As one of its agents, Faint knows that when given a direction and an order, "he was sent to kill, or not come back at all". Being an ex-SAS operative for quite a few years, Faint is more than capable of killing when needed, and he has shown he is also very good at finding his own way home afterwards.
For all his capabilities and accomplishments, Smith seems always on Faint's back. As Smith tells Faint when Faint pointed out that in the relatively short time he had been with The Company, he had certainly proven his worth, "You're a weapon, Faint. That's all. We point and you fire". After that rebuke and before Faint could offer much of a rebuttal, Smith also points out that, "You drink too much". Faint is aware there was no counter to that truth. Faint got bored easily and quickly and when there wasn't anything to challenge and excite him, he sought out and always found a bottle of something.