Dr. Watson

Dr John H Watson M.D. is a fictional character in the Sherlock Holmes books by Sir Arthur Conan Doyle. 
Dr Watson returns to England from the Second Anglo-Afghan War. He saves money on an apartment by getting a roommate who turns out to be Sherlock Holmes. When Watson finds out Holmes is a detective he starts to follow him on his cases and write down everything Holmes does. Dr Watson is the narrator of all the stories except one.
In many cases Watson plays an important part in the narrative. In "The Hound of the Baskervilles", for example, and in the long struggle against Professor Moriarty.
Early in the relationship, Dr Watson becomes engaged to marry Miss Mary Morstan, a former client of Sherlock Holmes (see "The Sign of Four"). Later it seems Watson's fiancée has apparently died. 
In "The Hound of the Baskervilles", Watson shows that he has picked up some of Holmes's skills at getting information from people. He observes to the reader, "I have not lived for years with Sherlock Holmes for nothing".