Mimi Masters is the daughter of Magic Priests David and Shanna Crowe. Her mother was later remarried to a man named Stanley which resulted in the birth of Mimi's half sister Selena. It is later revealed that Stanley was actually "Stanley the Demon"; who had plagued the Feeple family since the days of ole' when Jeremiah Feeple accused a Masters' ancestor of witchcraft. Mimi's ancestor cursed the Feeple family, stating every first born of the Feeple family will suffer a terrible fate before reaching sixteen years.
Mimi travelled to Hell to rescue Jeremy Feeple's soul from Stanley. In the process of her mission, the normally adorable and bookish girl got in touch with her dark side, as well as some very tight leather. At points it looked like she may not find her way back. Fortunately, Jeremy's pure soul and willingness to forgive Mimi revoked the curse.
Afterwards, Mimi relocated to Quagmire. Mimi spends most of her time in the library and is usually joined by her familiar, the somewhat cynical cat Aloysius.