"Who is Sherlock Holmes?"
Few people ask this question, because almost anyone could give an answer to it. Sherlock Holmes is one of those unusual literary characters who lives outside of his stories; ask that question, and most people will be able to tell you that he's a detective, distinguishable from other detectives due to the accessories of a magnifying glass, deerstalker hat, and pipe. He is as well-known by name as Santa Claus, Frankenstein, or Dracula. He is, as others have put it, "the world's most famous detective"; he's the detective to whom nearly all other fictional detectives are compared. Before we ever "meet" Sherlock Holmes in the books, we have an idea of who he is. But does this idea truly answer the question?
Interestingly, we're not the only ones who think we know Holmes before we've met him. In the very first chapter of A Study in Scarlet, Dr John H. Watson is a wounded soldier just returned to England; and, by chance, he hears of Sherlock Holmes through an old acquaintance, Stamford. Contrary to what you'd expect, Watson does not ask "Who is Sherlock Holmes?" Instead, he assumes he already knows what kind of person Holmes is ("'A medical student, I suppose?'"), and he would probably have stuck to these assumptions, were it not for Stamford's apprehensions ("'You don't know Sherlock Holmes yet'"). When later he finally meets Sherlock Holmes himself, Watson learns that Holmes is far from being the quiet medical student he expected him to be.
* * *
The entrance of any great character is usually a turning-point in the story, and often a representation of who the character is or what they do. On the surface, there is something surprisingly un-Sherlockian about Watson's meeting Holmes; and yet, simultaneously, there are elements in this introduction which are definitive of Holmes's character, as well as of Watson's role as friend and biographer. One of these elements is the subject of Holmes's "first lines", as it were.
"'You have been in Afghanistan, I perceive.'"
This sentence is often thought of as Holmes's first line in the series; however, it is really his third. His first line happens to be "'I've found it! I've found it'". These words are significant in many ways, but most especially interesting is the parallel (intentional or unintentional, I don't know) between Holmes and Archimedes--the mathematician who is famous for supposedly having cried "Eureka!" after finding "a method for determining the volume of an object with an irregular shape" (Wikipedia). Eureka translates to "I have found it" (Wikipedia). This is the first of at least three comparisons between Holmes and geniuses of Ancient Greece. Later on, in Chapter 2, Holmes is compared to Euclid, and again in Chapter 1 of The Sign of Four. Perhaps even more surprising is the fact that these parallels are made in the first two books of a very long series, before Holmes is shown to be a genius at solving numerous cases. And yet he lives up to it. He is a character who enters the story with perfect self-confidence, independent of Watson or the readers' approval.
Holmes's second line is very simple, and one which does not instantly seem important: "'How are you?' he said cordially". Its importance is, however, underlined by the fact that Holmes almost instantly resumes his previous exclamations regarding his chemistry experiment and discovery. In a way, one wonders why eccentric Holmes bothered with this formality at all, when he was in the middle of a momentous experiment and the deduction about Watson having been an army doctor. But was it just a formality? After all, judging from other stories, "How are you?" is not a typical greeting from Holmes. I can't help but wonder if, maybe, he really meant it, knowing as he did (via his deductions) that Watson was in poor health. If so, this would be the first of countless instances in which we see Holmes's philanthropic side, that part of his personality and principles which proves that we can't think of him as just being a cold, scientific "machine". Nor is he constantly depressed or stoic, either:
"'Ha! ha!' he cried, clapping his hands, and looking as delighted as a child with a new toy. 'What do you think of that?'"
[The Holmes book quotes are from A Study in Scarlet]