Mrs. Frisby is the main character of the book. She is a brave, daring widow with four children. Her husband, Mr. Frisby, died trying to help his friends, the rats. Now Mrs. Frisby has met the rats of NIMH and has been very willing to help them. She is even willing to risk her life to save Timothy, her youngest child. She met many friends in the book: birds, mice, and even rats.