In the first Holmes story, A Study in Scarlet (published in 1887), Watson, as the narrator, describes meeting Holmes, their subsequent sharing of rooms at 221B Baker Street, his attempts to discover the profession of his taciturn companion, Holmes's eventual taking of Watson into his confidence, and the events surrounding their first case together. Watson describes Holmes and his methods in detail, but to Holmes's taste, in too romantic and sentimental a manner.
Doctor Watson is a medical man of some experience. He had served in the military in Afghanistan, having been discharged following an injury received in the line of duty. In The Sign of the Four, Watson met Mary Morstan, who became his wife. Mary seemed a little less sure of her future husband, however, absent-mindedly calling him "James". Some have speculated that this is a wifely reference to Watson's unknown middle name, which could have been "Hamish".
Watson gives two separate locations for the Jezail bullet wound he received whilst serving in the army. In A Study in Scarlet he states "I was struck on the shoulder by a Jezail bullet, which shattered the bone and grazed the subclavian artery". However in The Sign of Four, Watson informs us "... [I] sat nursing my wounded leg. I had had a Jezail bullet through it some time before, and though it did not prevent me from walking it ached wearily at every change of the weather". The Adventure of the Noble Bachelor contains the only other reference to the injury. Here Watson is a little ambiguous he tells us "the Jezail bullet which I had brought back in one of my limbs as a relic of my Afghan campaign throbbed with dull persistence".
In Conan Doyle's original stories Watson is portrayed as a capable and brave individual -- "Quickly Watson, get your service revolver!". Watson's intelligence serves as a foil to Holmes's insight. Both are brilliant, and each is useful for their purposes, they are remarkably different in their function, a clever literary pairing. Watson occasionally attempts to solve crimes on his own, using Holmes's methods, however, because he is not endowed with Holmes's almost superhuman ability to focus on the essential details of the case, he meets with limited success, as Holmes remarks "Quite so... you see, but you do not observe."
The introduction of Dr. Watson in the Holmes novels, was a precursor to other similar characters. In the words of William L De Andrea,
In a number of film adaptations, in particular those featuring the comic skills of the actor Nigel Bruce, the character of Watson becomes more of a caricature. Far from being the able assistant as presented by Doyle, Watson is portrayed as an incompetent fool. Modern treatments have returned the roots of Conan Doyle stories and have portrayed a more sympathetic and competent Watson.