As I continue my own Appendix N project, reading the fantasy literature referenced in the the original 1979 Advanced Dungeons and Dragons Dungeon Master, I am struck by the number of stories that involve magical skulls.
Here are three examples, from books I am currently reading, or have just finished.
The Last Unicorn, by Peter S. Beagle, features a talking skull that reveals a secret passage to the protagonists, and who thirsts for a taste of wine, which he exchanges for the information, even though he can't actually taste anything.
The Magic Goes Away, by Larry Niven, features the animated skull of a Sorcerer. The Sorcerer cast a spell upon himself so that he could not die. Thus, even though his body has been destroyed, his spirit still resides within his skull.
Web of the Spider, by Andrew Offutt, features a magical skull, and when you peer through the bejeweled eyes of the skull, you can see the future.
I have not yet read even one twentieth of the Appendix N literature, yet at least three books have featured a magical skull. Is it any wonder, then, that The Tomb of Horrors should feature a skull, as the last intact remains of a former Wizard?
What is odd, is that there is no Skull artifact featured in the AD&D DMG.