Mary Elizabeth Morstan-Watson is the wife of Dr. Watson. Her father is Captain Arthur Morstan, a senior captain of the Indian regiment, and her mother is largely unknown, as she dies soon after Mary's birth. She has no other relatives in England, though she was educated there until the age of seventeen. Mary first meets Sherlock Holmes and Doctor John Watson when she brought the case of her father's disappearance in 1878 to them. She and Watson become attracted to one another during the events of the case, yet they refrain from pursuing this attraction until the case was finished. The doctor proposed and they married in 1889.
Described as a pale blonde, she had been making a living as a governess by the time she hired Holmes.
Morstan was created by Sir Arthur Conan Doyle. She made her first appearance in The Sign of the Four.