Here's why:
* His Actions: He's constantly trying to keep the animals in line and strictly enforces the zoo's rules, even if they are unfair. He also tries to keep the animals from escaping.
* His Personality: Mr. Skeevers is shown to be mean, grumpy, and uncaring towards the animals. He doesn't understand their needs and treats them more like exhibits than living creatures.
* His Role in the Story: The animals' desire to break free from Mr. Skeevers' control is the main driving force behind the plot. He creates a conflict that leads to the animals' rebellion and their journey to escape the zoo.
While the book is told from the perspective of the animals, Mr. Skeevers' actions and personality clearly make him the antagonist of the story.