Nicodemus isn't your typical leading man. In the story of his life, he wouldn't be played by Clooney or Denzel. Someone older, wizened, and more grizzled—someone with a tail—would probably play him. So maybe… Jeff Bridges? (Minus the tail.) In any case, the "black patch" that he wears over his eye and the "long scar" that travels all across his face really round out his appearance (11.35).
Of course Nicodemus doesn't start out that way. He wasn't always the tough, hardened rodent we see today. He began his life as just your normal, average rat—one that never thinks about anything more than where the next cheese nub will come from. He liked "games and jokes" (14.28). But after he is kidnapped and taken to NIMH, his intelligence skyrockets and he becomes the leader of a renegade band of super rats with super plans.
Now you might be asking yourselves why ol' Nicodemus gets the top spot among the rats. Who died and made him king? But we here at Shmoop think he's totally earned the throne. It's his wisdom, his strength, and his desire for justice and equality that make him such a good leader. His interest in fairness begins with his understanding of how much captivity stinks and extends all the way to helping the Frisbys, who aren't even members of his colony.
While Mrs. Frisby is the star of the mouse side of the story, Nicodemus is the star and main narrator of the rats' story. Almost everything that we know about the Plan, NIMH, and the rats' society, we learn from Nicodemus, who is one heckuva storyteller. He is also a brilliant rhetorician, which is a fancy way of saying that he makes great speeches.
In addition to being our guide and storyteller, Nicodemus is also the biggest fan of the Plan. When Jenner, his oldest and best friend, decides to bail on the Plan because he thinks it will be too hard, Nicodemus makes an impassioned plea for the importance of the Plan, going so far as to say, "We're just living on the edge of somebody else's [civilization], like fleas on a dog's back. If the dogs drown, the fleas drown, too" (22.57).
Nobody wants to be thought of as a flea, even a rat. Nicodemus believes that in order for the rats to progress, they have to move beyond what everyone considers rats to be. That is, even though they can survive by stealing and living "on the edges of human civilization," like rats usually do, he believes that in order to reach their full potential, they have to start fresh and be self-sufficient—in other words, they have to be less rat-like.
If you feel like this is some pretty heavy stuff, you're right. Nicodemus symbolizes the struggle that many leaders find themselves in when they are forced to defend a tough decision: life in the rat colony is easy. Life in Thorn Valley will be hard. Will his rats continue to support him if he keeps championing the tough route? All he can do is soldier on, hoping that his decision to be truly free and independent will prove itself to be the smartest, kindest decision in the end. To find out whether or not that proves true, we'll just have to go read the sequel.