How come the term "Karen" became an Internet video slang? Was it a person's name?

I don't know that anyone can go back that far into the origins to say.  Logically, someone must have been the first, but whether there was a bunch of made-up names used in the early times of the "karen" meme development and eventually Karen became the typical name to use, or if it started right out with someone just grabbing a name that worked, and Karen was it, or if the original stories were about an actual Karen, is not something anyone can ever truly know.

I suspect that many pseudonyms were used for the early "karen" stories, but people eventually just settled on Karen as a name that seems to work well, that somehow fits for some unidentifiable reason.

Somehow it was chosen, seemed to stick, and caught on (fell into use).