The Mouse King (also known as Rat King in some versions) is the main antagonist in the novel and ballet adaptation The Nutcracker. He is an oppressive ruler who wishes to rule over a magical kingdom where he comes from. He becomes successful as he transformed the prince into a nutcracker and overthrew him. The prince, however, still rebels against the Mouse King, as the story introduces the Mouse King and the Nutcracker Prince waging in a battle against each other, which soon brought the attention of the story's protagonist.
On Christmas Eve, a girl named Marie is visited by her godfather Drosselmeyer who persent Marie a nutcracker as her present. Marie enjoys the gift, but then her brother Fritz accidentally broke it when he wanted to play with it. Marie becomse upset and takes the nutcracker away from Fritz, as she promises to take care of it.
Marie's slumber is disrupted by the grandfather clock chimeing, and Marie belives Drosselmeyer is sitting on top of it. Around that time, the Mouse King and his army invades Marie's house. The Nutcracker soon comes alive and leads an army of toys into battle against the Mouse King. The battle is first in favor of the dolls, but they are soon overwhelmed by the Mouse KIng's army. Noticing the Nutcracker about to be taken captive, Marie throws a slipper at the Mouse King, fainting afterwards (cutting her arm on the toy cabinet's glass door in the process).
Marie wakes up in her bed the next morning with her arm bandaged. She tries to tell her parents about the battle between the mice and the dolls, but they don't believe her, thinking that she has had a fever dream caused by the cut from the glass. Several days later, Drosselmeyer arrives with the nutcracker after he fixed his jaw, and he tells Marie the story of Princess Pirlipat and Madame Mouserinks, also known as the Queen of the Mice, which explains how nutcrackers came to be and why they look the way they do.
The Mouse Queen tricked Pirlipat's mother into allowing her and her children to gobble up some lard….. that was supposed to be used in the King's sausage dinner! The King, furious about the now ruined dinner plans, had his court inventor, whose name happens to be Drosselmeyer, create traps for the Mouse Queen and her children.
The Mouse Queen, angered at the death of her children, swore that she would take revenge on Pirlipat. Pirlipat's mother surrounded her with cats which were supposed to be kept awake by being constantly stroked. However, the nurses who did so fell asleep and the Mouse Queen magically turned Pirlipat ugly (With a large head, a wide grinning mouth, and a cottony beard like a nutcracker.) The King blamed Drosselmeyer and gave him four weeks to find a cure. At the end, he had no cure, but went to the court astrologer.