Straight: Bob loves killing people, and becomes a hitman to make money off it.
Exaggerated: Bob works for free as long as he's allowed to kill people however he wants and whenever he wants. In fact he's willing to pay you for just for the opportunity!
Downplayed: Bob is a brutal thug who enjoys hurting people. However there's more to his character beyond that, and he's sane enough to follow reasonable orders and to understand that he needs money to survive.
Justified: The order that Bob trained with brainwashed all of its students into becoming psychopathically sadistic.
Carl the mob boss hires Bob on the recommendation that he is completely insane. Only to find out that Bob is barely coherent and unable to carry out an assassination with any dependability.
Unfortunately for Carl, Bob is also suicidal.
Then Bob stabs the Carl in the neck, and tells him he was the target all along while grinning.
Unfortunately for Carl, Bob takes Carl with him.
Parodied: Bob puts an ad in the paper reading "Murderous Lunatic Will Throw Chainsaws At Whoever You Want For Only $79.99 Each. 50% Off If You Let Him Skin Them Alive."
Bob likes both the money and the violence equally. Hence, he may accept the job for any of both depending on the situation.
Altenatively, for exaggerated version : He'd work for free if he gets to kill lots of people, but needs to take payed jobs from time to time because he has expenses like everyone else.
Bob accepts money up front for hits, but currently hasn't killed anyone in a good month, so the current one is on the house. He still requires coverage for bullets and other expenses though. On an impulse he shoots his potential client dead though, then takes all his money.
Bob does not enjoy violence, so he never hurts anyone.
Alternatively: Bob finds his job as a killer unspeakably dull, and only keeps at it because the money's good.
Bob is still insane, but he's not violent.
Enforced: This story is about a shadowy organization often has to use violent convicts. As expected, this trope tends to come up.
Lampshaded: "Where'd you find this new guy? Serial Killers R Us?"
Invoked: Carl wants an assassin who isn't just in it for the money, and who was crazy enough that any testimony he gave about who hired him wouldn't hold up in court.
Exploited: Carl is facing some budget cuts, so he stops paying Bob first, since Bob will just keep working for the hell of it.
Bob's violent tendencies are noticed early and treated.
Carl avoids hiring any assassin who doesn't regard it as "just business."
Discussed: "Perhaps we can buy Bob off when he comes after us?" "Not likely; he's in it because he likes it, and he hates missing out on his fun."
Conversed: "You'd think that character would be too dangerous to be worth it."
Bob owed more money to the mob than he could possibly pay back. Because of his formidable appearance, they put him to work collecting money for them. Over time, it was clear that he had a reluctant talent for hurting people. Eventually, he becomes a full-time assassin, but he can't live with himself after seeing what he has become. Eventually, Bob begins losing his mind, and accepting his role as a killer with manic glee. This addiction to violence prompts him to take on freelance jobs long after his debt to the mob has been repaid, and he can only vaguely remember the compassionate man he once was.
Alternatively: Bob's over-enthusiastic sadism and bloodlust mean that he gets himself and his employers killed or captured when a saner enforcer would have succeeded.
Reconstructed: Bob is completely nuts and needlessly sadistic, but he's also competent, and has his niche; he's called when his boss wants somebody not quietly eliminated, but blatantly slaughtered as a gruesome warning to others.
Played For Laughs: "Machete Bob" is hired. Carl's instructions are "I need you to kill...", before he can finish, Bob yells "Okay!" and decapitates everyone in the room. Then congratulates himself on a job well done, and asks the Carl's headless body for his fee.
Played For Drama: Bob slowly comes to realize that channeling his homicidal impulses towards specific, often deserving targets might be the only way to keep from killing everyone in sight. But it's not easy.