First, I talk about his characters. Let's imagine the characters of Sherlock Holmes. Generally, we imagine the tall and thin man with the pipe in his mouth. What Watson said in the stories is that he was nervous, polite, silent, and great musician. (Maybe his blood type is A.) He had a great concentration of the detective. He forgot everything (even having a dinner!) during the detective. His detective seems beyond our imagination. But it based logical and scientific proves. To put it briefly, he is the man who only do detectives. Its professional character interests the readers
Next, I point out the existence of Dr.Watson. He is typical English gentleman. He has common sense. and he is honest, kind and a little foolish. But he plays many important rolls in the stories. He is a storyteller, listener, assistant, bodyguard, adviser, and so on. We apt to think him a simple man. But he is not a simple man we suppose to. and we see Holmes through the Watson's view. Because of it, we can read his stories in relief. So we can read his stories from young to adult, from men to women.
Finally, I refer to the " World "of Sherlock Holmes. He lived in London in Victoria era. There are many chariots named "handsome" on the street. The Baker Street is in the thick fog. The gaslights turned out. In this mood the accidents happen and the mystery starts... these mood caused an uncanny atmosphere and I think its atmosphere fascinate the readers.
I have written down about Sherlock Holmes, above all the popularity of Sherlock Holmes.
The first topic is his remarkable character. His character fascinates the readers.
The second is the existence of Dr. Watson. His existence relief the readers.
The final is uncanny atmosphere in the Victoria era. Its atmosphere fascinates the readers.
So these points make Sherlock Holmes famous and popular with the people in the world.