Holmes' foe (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
(Other definitions for moriarty that I've seen before include "Holmes' arch enemy" , "The Napoleon of Crime (Conan Doyle)" , "Professor . . . . . . . . was Sherlock Holmes's greatest enemy" , "Arch-enemy of Sherlock Holmes" , "Sherlock Holmes' The Napoleon of crime" .)