Simon Scarlet is an agent with the British Secret Service.
The agency is really MI6 but Scarlet always refers to it by the other name for some reason. He has been an agent with them for a few years as shown by the fact that he has completed a good number of missions successfully for them. Since he is described several times as young looking, though, we must place his age likely in his late 20's.
Scarlet definitely lives up to his name in that he is redheaded. He is described as having a "tanned, freckled face" and as being "quite cute". It is also thought by a young woman who watched him walk away that "his tush wasn't shabby, either".
Though fully aware of the dangers of a mission, Scarlet is also able to note the humor of some situations and manages to react accordingly with a droll comment or two. Usually those dealing with him at such moments do not take his witticisms well but that does not stop him from expressing them.
His calm demeanor, as well as his British accent, work wonders in calming people down which is a good thing because where he goes, there is usually a good deal of un-calmness. Before defusing a bomb, he sips on a martini ("it's always time for a martini") and remarks, "I'm a British secret agent ... I survive on a diet of martinis and casual sex".
As the short series progresses, Scarlet will have to go contrary to his own agency's wishes and that gets him into enough trouble to need the help of the CIA, something he is not happy with since he views them almost as the enemy but you do what you have to survive.
Fun statement by Scarlet when he states that nowadays, England is like "George Orwell's 1984 without the irony".