Penelope Poisonfur is a recurring character in the Geronimo Stilton Books.
Poisonfur can be highly ordering, especially in a boot camp as a leader of it. She forces her trainees to do something. If not, she will say, "Do it, or you will be sorry!" She is, surprisingly, Geronimo's Pychologist's neice.. He said he was sure it would work. He also says that she was the only one who could help him. He also says her methods can be a bit wacky.