The Catholic nun at St. Theresa's Orphanage where Remo was left as a baby. Sister Mary Margaret formed the early years of Remo's life, and her advice serves him well in the future. Often when Remo faces a tricky situation, he remembers her lessons.

Remo thinks that Sister Mary perished when St. Theresa's burned - but she survived. It was lucky for Smith that Remo never discovered that CURE was behind the arson that destroyed St. Theresa's.

Conrad MacCleary placed Sister Mary in a nursing home after the fire. She never fully recovered. Sister Mary's one regret in life was the one soul she lost - Remo Williams. In #100, Remo discovers that she is near death and rushes to her deathbed. Sister Mary discovers the truth about Remo, and dies content, with Remo at her side (#100.)