Nicodemus is the leader of the rats. The leader or Nicodemus was chosen as they were leaving NIMH. He shows kindness to everyone but to Mrs. Frisby by helping her to move her house. Nicodemus was the rat witht he idea to move to Thorn Valley and stop living a life of robbery. Without the hlpeof Nicodemus the rats and Mrs.Frisby would still be living a harsh life. Going to NIMH may have saved his and many others lives.