Here's why:
* Unchanging Values: Zaroff's core beliefs and motivations remain consistent throughout the story. He is a sadistic hunter who finds pleasure in the thrill of the hunt, specifically in the pursuit of humans. This desire never wavers, even as he faces challenges from Sanger Rainsford.
* Lack of Development: Zaroff doesn't undergo any significant internal change. He shows no remorse for his actions and remains confident in his hunting abilities. He even argues that his cruelty is justified by the excitement it provides him.
* Contrast with Rainsford: While Rainsford begins as a hunter, he evolves throughout the story, questioning his own morals and ultimately developing empathy for his prey. Zaroff, on the other hand, remains fixed in his amoral worldview.
While Rainsford is the protagonist and undergoes a significant transformation, Zaroff's unchanging nature makes him the static character, serving as a foil to Rainsford's development.