His physical appearance is that of a large, wolf-like creature, capable of speech. The film shows him as having short, dark, blue-black fur and luminous green eyes, as well as more fangs than those of an ordinary wolf.
Gmork's primary mission in the Neverending Story is to track down and kill the young warrior Atreyu. In the book, he never manages to catch up with Atreyu, because the latter uses the magical powers of the monster Ygramul's poisonous bite to travel instantaneously to the Southern Oracle. In the movie, Gmork almost manages to kill Atreyu in the Swamps of Sadness, but Atreyu is rescued by Falkor.