As is the case with many members of The Old Guard, little that is concrete is known about the late Doctor Lucifer Mongfish, apart from his relationship to the current protagonist; in this case, he is Agatha's maternal grandfather. However, before Lucrezia Mongfish apparently converted to the cause of Good and married Bill Heterodyne, we are assured that there are many stories of The Heterodyne Boys having occasion to foil the Evil Dr. Mongfish's plans, and those of his daughter.