I think the relationship between these two famous literary figures is captured through the way that Sherlock Holmes and Dr. Watson actually act as foils for each other in all of their adventures. A foil is a character that is placed next to another character for purposes of comparison. Of course, if you have two characters paired like this, the extremes of each are emphasised and exaggerated. Think about the relationship of these two characters: what is notable of course if the fierce intelligence of Sherlock Holmes that Dr. Watson can never attain. When Dr. Watson tries to use his skills to deduce facts, he is always shown up by Sherlock Holmes. Yet at the same time, Watson possesses a fierce loyalty to Holmes that Holmes is forced to depend upon to solve numerous cases. The two characters need each other, but also Watson's ignorance emphasises the intelligence of Sherlock Holmes.