Psycho for Hire/Playing With

Basic Trope: An assassin who kills because they enjoy it. The money is secondary.
 * 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.
 * Justified: The order that Bob trained with brainwashed all of its studenets into becoming psychopathically sadistic.
 * Inverted: Bob is a surprisingly stable individual who sees killing as a business transaction and a necessary evil.
 * Bob is a reluctant assassin that likes to avoid getting his hands dirty as much as possible, but it's willing to do almost anything for a hefty sum of money.
 * Bob is an extremely happy individual that likes doing random acts on kindness for other people, not for a material reward nor the recognition, but to make world a better place.
 * Subverted: A Smug Snake 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.
 * Double Subverted: Then Bob stabs the Smug Snake in the neck, and tells him he was the target all along while grinning.
 * 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."
 * Deconstructed: 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.
 * Zig Zagged: 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.
 * Averted: 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.
 * Lampshaded: "Where'd you find this new guy? Serial Killers R Us?"
 * Invoked: The Big Bad 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.
 * Defied: Bob's violent tendencies are noticed early and treated.
 * The Big Bad avoids hiring any assassin who doesn't regard it as "just business."
 * Played For Laughs: "Machete Bob" is hired. The Contractor'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 contractor'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.
 * 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."
 * 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.