As paranormal villains go, Douglas Montgomery is one nasty dude. He's controlling, manipulative, and willing to do whatever it takes to give himself the upper hand—even if it means killing people. To Sam, Douglas is a "predator," and "With predators, if you move, if you're seen, you're eaten, and this man in his expensive but understated gray suit could swallow me whole" (1.119). Whoa. Even just seeing him, without knowing anything about him, gives Sam the willies.
A villain this evil has to come from some pretty interesting beginnings, and Douglas definitely does. As a child, he discovered his necromancy powers when he saw the spirit of his dead cousin at the cousin's funeral. His Aunt Lynn took him under her wing to train him, explaining that "Left alone […] their kind could destroy themselves" (3.30). The reality, though, is that Douglas ends up more destructive as a result of his alliance with Aunt Lynn since he ends up killing her and stealing her powers. Oops. It's a ritual he's repeated in his dungeon of doom with numerous other victims, and now he wants Sam to join the club.
Aside from his insatiable desire for more power, Douglas is also obsessed with controlling the members of the Council, the national underground network of paranormal creatures. As head of the Council, he's kind of a big deal, even though people generally don't like him because of his manipulative tendencies. Sam, however, presents a major obstacle to his position. We're told:
The last thing he needed was to give the Council an excuse to remove him as leader, and a rogue necromancer was a very good excuse. (3.35)
With Sam roaming the streets of Seattle unchecked, it would be easy to blame Douglas for the oversight, and since Brannoc already has it in for him, Douglas figures it's best to eliminate Sam rather than play with fire.
Seriously, though: Douglas is totally evil. In an act that elevates him to the corruption of the mafia, he kills Brooke and sends her head to Sam in the mail. He also kidnaps Sam and abuses him while teaching him to use his powers, and he even raises a guy from the dead only to force him to clean the dungeon and "reenact his own death" (20.86). We here at Shmoop would like to say we take no pleasure in the deaths of fictional characters, but when Douglas bites it, well, it's hard not to crack a smile. Good riddance.