Her real name is Madeleine Frye, but her friends call her Maddie.In public, she is Maddie Ballinger.
Maddie has brown hair, long legs, and is told to be skinny. In the seventh grade, Maddie was known for a high messy bun which the other girls started to wear, and they called it the Maddie Frye Frizzle Bun. This is stated in the first book, Behind the Gates.
One of Maddie's most referred to attributes (usually by Rosie Chavez) is that she complains quite a lot. She also is not the most athletic girl you might come across. Despite this, she is shown to be a loyal friend to Louisa Ballinger, and listens when she is in danger.
In Behind the Gates, she is often described as moody and whiny, but in the later books, she is defined as independent and courageous.
After being kidnapped by the Alliance and taken to the Phoenix Center, Maddie changes because of the drugs they gave her for brainwashing.
In With the Enemy, Maddie learns that her mother is the Hornet—leader of the Resistance. She is given a task to give her mother a box.