Short answers, pulled from the story.
Arthur Conan Doyle published The Final Problem in 1893 in which Sherlock Holmes fell to his death at the Reichenbach Falls. He resurrected the character in 1903 with The Adventure of the Empty House after public outcry forced him to write a story explaining that Holmes had faked his death to escape Professor James Moriarty.
The Great Hiatus refers to the period between 1891 and 1894 when Sherlock Holmes was presumed dead after the events of The Final Problem. The earliest known use of the expression Great Hiatus dates to 1946 and covers the time from his disappearance to his reappearance in The Adventure of the Empty House.
Irene Adler was a retired American opera singer and actress who bested Sherlock Holmes in a battle of wits in A Scandal in Bohemia. She escaped Holmes before he could retrieve the photograph of her and the Crown Prince of Bohemia Wilhelm von Ormstein, proving that emotional matters opposed the cold reason Holmes placed above all things.
Sherlock Holmes lived at 221B Baker Street in London with Dr. John H. Watson and their landlady Mrs. Hudson. The two men worked together for seventeen of Holmes's twenty-three years as a detective, with Watson serving as his biographer and companion despite disapproving of Holmes's cocaine habit.
The Sherlock Holmes Museum opened on Baker Street in London in 1990 and a second museum opened in Meiringen near the Reichenbach Falls in 1991. By the 1990s over 25,000 stage adaptations films television productions and publications had featured the detective making him the most portrayed human literary character in film and television history.
Sherlock Holmes never utters the phrase Elementary my dear Watson in any of the sixty stories written by Sir Arthur Conan Doyle. The exact phrase and close variants first appeared in newspaper and journal articles as early as 1909 and one of the nearest approximations appears in The Adventure of the Crooked Man.