I've been watching the "King of Queens" sitcom where, as you may know, the protagonist's last name is Heffernan. So I got interested in the origin and etymology of the name and it turned out to be that it's Irish and has the meaning "demon". That's what the WIKI says:
"The name Heffernan is derived from the Irish Gaelic name O Heifearnain, which comes from the given name Ifearnan meaning "demon"".
Any ideas of why a person could be called a "demon" in the faraway past?
What I mean here is that usually in Chrisitan culture such names as
Demon disappear with time as having negative connotation.
It was strange to me that such name could survive the time and stay in use.
However, as it turned out to be, the etymology is a bit more complex than I thought.
Here is a link: