The NIMH (National Institute of Mental Health) Corporation was the Big Bad of the entire Secret of NIMH series and was based very loosely on a real-world company of the same name; however, the name is where the similarities end and the fictional NIMH is considered (at least by animals) as one of the most evil places in the world. If one were to be picky, one could say that NIMH is the true main antagonist of the series, since they are responsible for the creation of the villains of the series.