Mrs. Hudson (her first name is unknown, but she is often called “Martha” on the assumption that she is the housekeeper who infiltrated the German spy Von Bork’s household under Holmes’s direction in “His Last Bow”) is the landlady of 221 Baker Street. Ordinarily, she performs housekeeping duties, provides meals, delivers messages and correspondence, and occasionally ushers in clients. Some have interpreted Holmes’s remark that “she has as good an idea of breakfast as a Scotchwoman” (NAVA) to mean that she is a Scot, but I find the argument unconvincing and there is no other evidence on this point.
Mrs. Hudson is fond of Holmes despite “[h]is incredible untidiness, his addiction to music at strange hours, his occasional revolver practice within doors, his weird and often malodorous scientific experiments, and the atmosphere of violence and danger which hung around him” (“The Adventure of the Dying Detective”). The detective’s reappearance after three years threw her into violent hysterics, but by evening she’d recovered sufficiently to play a crucial role in setting a trap for Moriarty’s last known lieutenant.
Does anyone know if canon states that Mrs. Hudson is a widow? I have that impression, but it may be fanon.