A rather gruff woman, Madame Christmas is the proprietor of a hostess bar in Central City frequently patronaged by Colonel Roy Mustang. At first, it would merely seem that this bar is further proof of Mustang's unapologetic debauchery, but it becomes quite apparent that the women under Madame Christmas' care act as secret informants to Mustang and his squad and that Madame Christmas herself is a skilled intelligencer and contact between Roy and Lt. General Grumman in East City.
It has been recently revealed, by a secret investigation into Roy's past carried out by Central Command's agents, that Madame Christmas' real name is Chris Mustang and that she is Roy's foster mother.
In Character Guidebook 3 released recently in Japan it's revealed Chris Mustang is actually the younger sister to Roy's biological father, making her his aunt. According to this guide, she took Roy in after the death of both his parents, when Roy was still very young.