I'm vaguely familiar with the RPG anecdote the [Head of Vecna](https://en.wikipedia.org/wiki/Vecna#Head_of_Vecna). Is there more to this tale? Why is this story important to RPG culture?

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***Note:*** In Comments on this [question](https://rpg.stackexchange.com/q/98723/8610) (now deleted but available on Meta as part of this [question](https://rpg.meta.stackexchange.com/q/7040/8610)), I mentioned the Head of Vecna (along with a few others) as an RPG touchstone, but when I told what I knew of the Head of Vecna story (which was about as much as the summary on the Wikipedia *page) to my son, a budding yet enthusiastic gamer, I didn't have many details to flesh out the tale nor was I entirely clear on the story's influence or ultimate point.*