Character Analysis
Bad to the Bone
Let's work backward, shall we? Nailer kills his own father to survive. And then he's not sure how he feels about it. In the last chapter, Nailer and Sadna talk about what Richard was like in life:
"He was bad news," she said. "I don't say that about many people, but Richard Lopez left a lot of hurt behind him."
[…]
His dad had been crazy and destructive and if he was honest, downright evil. But now that he was dead, Nailer couldn't help remembering other times as well, times when the man hadn't been high, when he'd laughed at jokes, when they'd roasted a pig on the beach, good times. (25.3-5)
Some might say that Richard deserves what he gets in the end, but Nailer still has complex feelings about the man. Sure his dad was evil and violent and an addict, but he was still Nailer's father, and since his mom's dead already, he's Nailer's only official family. Doesn't that count for anything?
Nope, not really. Richard never acted like Nailer's father. He'd disappear for weeks at a time, and when he was home, he'd beat Nailer and take what little Nailer earned. He never offers Nailer the safety and security that we often associate with family. So while it would be incredibly difficult to imagine Pima killing Sadna, it's much more believable to imagine Nailer killing a man who never really acted as his father.
"For the Love of Money"
Greed is the only thing that motivates Richard; he wants moolah, and he's willing to do pretty much anything to get it. (Though, truth be told, we're never sure if he wants drugs more than money, or money more than drugs.) He's willing to kill innocent people and even his own son in the end, because for Richard, the means justify the ends. If he wants something, he up and takes it. In fact, Sadna gambles that he's even willing to forgive Nailer's slaying of Blue Eyes and escape. She advises Nailer:
Broker a deal and sell the girl to those people down there, and Richard will forget. You don't think so, but money will make him forget plenty. (14.119)
For Richard, money is what makes the world turn. It's the only currency (pun totally intended) that he understands; he has no concept of compassion or empathy or morality or humanity.
But he does, however, understand both fear and violence.
Perfect Killer
There is lore built up around Richard Lopez, and he's legendary for his quickness, for his violence, and for his unpredictability. Check it out:
"I saw him kill in the ring," Pima said. "Beat him down and killed him, even after everyone said he'd already won. Beat him bloody, left him with his head cracked open." (12.9)
This is indicative of Richard's explosive and violent anger, and his general lack of regard for human life. In fact, some (ahem, us) might say that Tool is more human than Richard Lopez. Any life except his own holds no meaning for Richard, even his own son's. As he hollers at Nailer:
He bared his damaged teeth. "I'm going to spread your guts on the floor!" (24.157)
Super terrible, right? In the final confrontation, Richard is more than willing to kill Nailer. And this, more than anything else that he's done, strips away his humanity and any sorrow we might feel at his death.