For those in that last group, Vermithrax Pejorative is a dragon. The dragon in the movie Dragonslayer to be exact. Now, I must go on record as saying I didn't care for the movie at all. I just saw it recently and thought it was significantly subpar. The dragon, however, is still one of the greatest movie dragons of all time. It exuded pure malevolence and reptile wickedness. It looked like a dragon should look. It was all scales and spines and fire. There was no cuteness or adorable eyes or anything else that would make you feel bad that our protagonist was determined to kill it. Live and let live? Not a chance. In this movie, with this dragon, it's kill or be eaten.
That's not to say that there isn't a place for the noble dragons of other films and television. Draco in Dragonheart was a great character. I rather like the dragon in Merlin as well. However, they are sympathetic characters, even when acting with deliberate malice. You don't want to root against them, despite the fact that they sometimes try to kill the good guys. It's just hard to hold that against them.
Enter Vermithrax. So evil, so malevolent, so powerful that it is even given an ugly name. Its name means "The Wyrm of Thrace that makes things Worse". I don't know about you, but that doesn't sound very warm and fuzzy to me. It sounds like the Big Bad that everyone wants to avoid. You know just from his name that no matter how bad things are, he's going to make them worse. And that is what makes him an effective movie dragon.