I agree Gmork is definitely not the major villain of The Neverending Story. He's "servant of the power behind the nothing", but The Nothing isn't a weapon, it's more like the realization of a metaphor inside Fantasia. There are people in our world, who (for example) push for engagement at all costs, and don't care about what the results are—and that poisoning of peoples' hearts is what in Fantasia becomes the nothing. The dialog between Atreyu and Gmork is longer in the the book, and one thing it mentions that I don't believe the movie does, is that when the creatures of Fantasia fall into the nothing, in the real world they become lies.
> 'When your turn comes to jump into the Nothing, you too will be a nameless servant of power, with no will of your own. Who knows what use they will make of you? Maybe you'll persuade people to buy things they don't need, or hate things they know nothing about, or hold beliefs that make them easy to handle, or doubt the truths that might save them.
It's really an excellent passage.
Anyway: the movie covers only about the first third of the book, and the book is quite wonderful, and I highly recommend it. I love the movie, too—I'm glad we have both.