Who is Ignacio Carrera from The Key to Midnight and what is their importance?

Ignacio Carrera is a crazy body builder, who is also a hired killer for the Russians. Carrera likes pain, inflicting it as well as feeling it. Carrera has fantasy about killing people and hopes that if Joanna undergoes the brainwashing techniques a second time and is left brain damaged, he will be allowed to keep her as a plaything. However, before Joanna can begin the treatment again, Alex gets free of his bonds and shoots Carrera. Carrera has conditioned himself to withstand great amounts of pain, so the bullet does nothing to stop him. Carrera goes after Alex. Alex manages to get outside the house and Carrera follows. Alex and Carrera fight in the woods and Alex manages to wound Carrera fatally, but still he will not go down. Finally, Alex breaks Carrera's neck.