In Harry Potter most of the people are afraid to say Voldermort's name and they use the alias you-know-who.
I'm looking for other characters whose names are even feared by the public in fantasy stories. A candidate that is feared that much by the common folk could be Sauron, but his name is spoken many times in LoTR without any fear.
This looks like a list question but I'm not looking for a complete link, just examples.
- I'm also interested in real world examples of this, but that might be out of topic for this site, thus you don't have to include them in answers.