NIMH (National Institute of Mental Health) are scientists from the place with the same name. They are the titular antagonists in The Secret of NIMH. The fictional NIMH is based on the real world organization. They are also responsible for capturing Nicodemus and other rats. In The Secret of NIMH 2: Timmy to the Rescue, Martin who was mutated by Dr. Valentine becomes the Leader. In Carmen, the Story of NIMH is first seen being told by Emperor Nod.
Roster
- Dr. Valentine (Leader)
- Martin Brisby (Leader in the Sequel)
- Muriel & Floyd (Leader in the Sequel)
| The Secret of NIMH |
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 Characters: Mrs. Brisby | The Great Owl | Jeremy | Nicodemus | Mr. Ages | Auntie Shrew | Justin | Jenner | Sullivan | Teresa Brisby | Cynthia Brisby | Martin Brisby | Timothy Brisby | Brutus | Jonathan Brisby | Farmer Paul Fitzgibbons | Mrs. Beth Fitzgibbons | Billy Fitzgibbons | Dragon | Miss Right | Jenny McBride | Cecil | Joseph Valentine | Muriel & Floyd Songs Flying Dreams | My Life and My Love | Come Make the Most of Your Life | I Will Show the World | Magic Mystery Show | Just Say Yes! | All I Had is Gone |
