In general, videogame protagonists need a set context for their lives before being thrust into action and adventure. Mario can't just be a dude with a goomba-stomping fetish; he has to be a plumber. Marcus Fenix can't just be some chainsaw-wielding jerk; he needs to be an ex-soldier. For better or for worse, most game characters need some sort of backstory, often encapsulated in the character's profession.
But what about the characters whose professions have almost no impact on the way they act once in the actual game? What about those heroes and heroines who claim to do one thing as a source of their income, but actually do another? What about this videogame characters who suck at their jobs?