Who was the Mouse King in the play?

The Mouse King in the play is a character often portrayed as the antagonist, bringing conflict and tension to the story. In various adaptations, including "The Nutcracker," the Mouse King is depicted with a mix of cunning and malice, often leading an army of mice against the heroic figures.

In the context of this question, Gus is recognized as the character that embodies this role, providing a clear representation of the Mouse King’s attributes and actions. This connection helps to deepen the audience's understanding of the play's themes of good versus evil. The other characters mentioned do not align with the characteristics or functions of the Mouse King, which solidifies Gus's role as the correct answer.