Nicholas Ruskin

"(Kate: What do you want from me?) Everything."

- Casanova "You're here to fall in love, to experience love. But now I need you to listen very carefully, and take what I say very seriously, alright? Don't try to escape. Don't cry out for help. And do not try any of your kickboxing tricks. Now I'll do what I can to help you not break these rules, but if you do Kate, you will really disappoint me. There now. See. That didn't hurt did it? Don't worry. You're with Casanova."

- Casanova explaining his rules to Kate as he is sedating her "Good night, sweet Kate."

- Casanova's last words. Casanova (real name: Nick Ruskin) is the main antagonist of the novel Kiss the Girls and its 1997 film adaption. He was a serial killer who kidnapped beautiful women while working as a police detective.

He was portrayed by Cary Elwes in the film, who also played Lawrence Gordon and Edgar.

Book
Not much is known about his past or how he he came to be how he was. What is known is that when he was a teenage boy, he snuck into Coty Pierce's, a girl he went to high school with, home where he spent his time in the attic, watching her and her family through the vents. One night, he finally decided to sneak out of the vents to commit "the perfect crime", and raped and killed Coty, her sister, and her mother.

Some time later, he met Will Rudolph in college. It's not explained how, but he found out that he had stalked and killed a young couple and kept the woman's tongue as a souvenir. He then convinced him he could trust him. The two then formed a bond and began on their own murder sprees together.

He eventually became a detective for the Los Angeles Police Department, which not only deceived the cops as he gained their trust, but also gave him the chance to change the dates of the kidnappings so he would have alibis. He was also married, but had somehow managed to go on his killing sprees without her knowing.

Unlike his accomplice, Will (aka The Gentleman Caller), who was very brutal and cold blooded in his nature, Nick was more calculating and reserved, selecting women based on both physical beauty and their personality. In his mind, they loved him as well. After he kidnapped them and took them to his lair, he would rape them and make sure they didn't brake any of his rules, which meant trying to escape or talking to each other. He apparently suffers from Dissociative Identity Disorder, as he wears different masks depending his personality. If any of the girls broke his rules, he either kill them via lethal injection, or take them to the woods, tie them to a tree, cut their hair off as his own way of punishment, and leave them to die. He'd rape them one last time before leaving them, as well as take off his mask to reveal his face to them. He seems to feel empathy and remorse for them as he does so. However he tries his best to put those feelings aside and convinces himself that they are to blame for their own deaths.

Nick eventually meets his demise when he kidnaps Alex Cross' daughter, Naomi, as well as Kate McTiernan. He seems to value Kate the most. After Kate escapes, she encourages Alex to track him down even further after she informs him that she spoke with Naomi. Time passes on as they discover more clues leading to their discovery of The Gentleman Caller. As they get closer, both Nick and Will  break into Kate's house and beat her into a coma for a while. Later in the novel, Alex and his partner, Sampson, discover where they are both keeping the women and make it to their hideout. Nick and Will are both watching them and take Sampson out while Cross finds Naomi. Cross hears Sampson scream and runs to find both Nick and Will, wearing masks, on top of his partner with a knife stuck in his back, but still alive. Cross takes his gun out and fires at them, hitting one on the shoulder. The two take off running and make it to a nearby bar, steal a truck and drive off. Cross takes a car and goes after them. In traffic, the two run out of the car, running opposite directions and firing their guns. Cross follows one, they exchange gunfire, and he hits him in the chest. Cross runs to the man and takes off his mask, revealing him to be Rudolph. He dies telling Cross that he will never catch Casanova. This results in him going into a breakdown after losing his "twin". Once Kate is out of her coma, Alex visits her,  goes  jogging and finds a dead FBI agent. He runs back to the house where Nick hits him with a stun gun. With Cross down, he heads for Kate, but Kate fights him and takes him down. He takes out his gun to shoot her, but Cross gets up in time to shoot and kill him in self-defense.

Movie
In the 1997 film adaption, not much is changed about Nick Ruskin's character or his backstory. Although, how he met Will Rudolph is omitted, as well as them putting Kate in a coma, and his marriage to another woman. He is also shown to be slightly more evil, given that he sees Will as expendable and nothing more than someone to share his crimes with. This is evident when he nearly shoots him to death for showing fascination over his "collection" of women in his lair. There's also no hint of him possibly feeling empathy or remorse for his victims as he kills them. His death is changed as well. After he goes over to Kate's house to cover for the next police shift, he reveals himself as Casanova and they engage in a fight. He overpowers her for a while and attempts to rape her. However, she gains the upper hand and handcuffs him to her stove. Unfortunately, he grabs her kitchen knife and slits her arm, weakening her. He then tears out the glass tubes and attempts to blow them both up with his lighter. When Cross arrives to try to talk him down, Nick gives a speech about how he feels his "animal self" come alive any time he looks at a beautiful woman and that he merely wants to break them down through rape and torture, and how Cross, deep down, is no better than him. He also taunts him about how he raped Naomi the whole time he had her in captivity for more than a week. He attempts to turn on the lighter, but before he can do so, Cross manages to shoot  and kill him through a milk carton so the muzzle blast from his pistol does not ignite the gas.