Sherlock Holmes’s mortal nemesis was Professor Moriarty.
Harry Potter’s nemesis was Voldemort.
Doctor Who had a nemesis named Morbius. So did Spider-Man. Morbius was also the name of the antagonist in The Forbidden Planet.
Frodo Baggins went through the mines of Moria to get to Mordor, where he met Sauron, who, as great a villain as he was, started out as the lieutenant of Morgoth, the original and darkest villain in the world of Tolkien’s Middle Earth.
H.G. Wells sent his time traveller into the future to encounter a cave-dwelling evil race called the Morlocks. He also created an evil genius called Dr. Moreau.
King Arthur was betrayed by Mordred.
The really scuzzy city in Terry Pratchett’s Discworld series is Morpork.
So what’s the deal with “mor”? Is there something to the syllable that suits it for melancholy, darkness, and villainy?