Why does Watson call Moriarty the "Napoleon of Crime"?

At the end of The Seven-Per-Cent Solution we learn that Holmes's obsession with Moriarty comes from his suppressed childhood memory of Moriarty's affair with Holmes's mother when he was his teacher (after which Holmes's father killed his mother). But after learning this, Watson says to Freud:

The Napoleon of Crime. Holmes was right about him from the very beginning, Professor Moriarty I mean.

Referencing the nickname Holmes gave Moriarty earlier, when he thought him to be a criminal mastermind. But what does he mean with this statement, given that Moriarty was not the criminal genius that Holmes made out of him, but just a timid little mathematics teacher that had an affair with his mother. So he wasn't "right about him from the very beginning". Is he merely saying that this was as heavy a crime (especially given that it lead to Holmes's mother getting killed), or does he mean something else with this line (maybe in reference to the real Napoleon)?

Best Answer

Napoleon Bonaparte was a notorious womanizer, and his antics have been recorded in numerous books and documentaries.

According to 'Napoleon and his Women', by British historian Christopher Hibbert, Napoleon would often weaponize his sexual experiences for leverage and political power, making him effectively a gigolo, although its a stretch to apply this handle to the Emperor.

Even though Napoleon existed in the time before tabloid journalism, court gossip was powerful enough to consolidate this reputation internationally, and it could well be this that Watson is referring to.