Poul Anderson (1926-2001) is much better known for his Science Fiction tales, but he does have three (well, 2.5) fantasy stories on the Appendix N list, and two of these feature witches rather prominently: "Three Hearts and Three Lions" and "The Broken Sword."
I will take each in turn and also expand a little from "just witches" with these.
Three Hearts and Three Lions (1953)
Anderson’s Three Hearts and Three Lions is already famous in D&D circles for giving us Law vs Chaos, the Swanmay, regenerating trolls, and even the proto-paladin in Holger Carlsen. But nestled amid the elves, trolls, and Moorcock-before-Moorcock cosmology is one of the first proper "witches" of Appendix N.
The unnamed witch of the forest hut is classic fairy-tale witchcraft: ugly, corrupt, but wielding real power. She brews potions, dabbles in deviltry, and represents the Chaos side of Anderson’s moral spectrum. Anderson clearly has one foot in the folkloric hag tradition; this witch could have walked right out of the Brothers Grimm, but her function in the story is thematic as much as narrative. She exists as a living symbol of the Chaos that Holger is pitted against, an incarnation of superstition and malice. While her interactions with Holger are not long, she is his first clue that magic, chaos, and evil are real, tangible things in the world/time.
Then there is Morgan Le Fey. She is Holger's former lover in a past life, and she is the main antagonist. She is a representative of the "Old Ways," the paganism of Europe, dying out in the face of rising Christianity. She is also representative of chaos, evil, and magic. Where the old hag is evil and ugly, Morgan Le Fey is evil and beautiful. Representing that evil does come in many guises and our hero needs to recognize that.
The battle is a parallel of the one Holger left in his time, World War II.
Both witches represent the two types of witches most often seen: the old Satanic Hag and the beautiful Pagan. Both, however, represent evil and mostly Chaos.
The notion of Paganism/Old Ways versus Christianity is a recurring theme in Anderson's other significant Appendix N book.
The Broken Sword (1954/1971)
The Broken Sword gives us a much darker, more primal vision of witchcraft.
Here we get another hag-witch who is close enough to the elves and trolls to have dealings with them, but is also very explicitly Satanic. She lives in a run-down cottage/hut, deals with the dark forces of evil, and has a talking rat familiar. Honestly, she could even be the same witch if so many years were not between them.
She also tempts our main antagonist, the Changeling Valgard, by glamouring herself into a beautiful woman. It is her desire for vengeance that sets the plot into motion.
Like Three Hearts, the Witch, and she never is given a proper name, is a force of evil and chaos. Also like Three Hearts, the story centers around the battle between Pagans and Christianity, which Anderson casts here as Evil/Chaos vs Good/Law, respectively.
The elves and trolls of The Broken Sword are more similar to each other; both are forces of Chaos, for example, and an elf/troll child is a Changeling. Their magic is also described as akin to witchcraft ("witchsight" allows humans to see the world of faerie) and to the witchcraft the old hag employs. Many elves and trolls have "Warlocks" in their ranks.
Here, also, the big Pagans vs. Christians war takes a back seat to two warring factions of Pagans, the Elves/Faerie and the Trolls/Giants. The interaction our protagonist Valgard has with the displaced Faun is very telling. This area of England/British Isles is one of the last holdouts of the Pagan ways.
The mixing of the various mythologies, Norse, Irish, Welsh, British, and Greek, is very D&D.
That Last Half
I joked above, 2.5 books in Appendix N. The ".5" is "The High Crusade" which is more appropriately a Science Fiction or Science Fantasy novel. I didn't include it here because, simply, I have not read it.
A Note About Trolls
Three Hearts and Three Lions is notable for giving us the "D&D Troll," but the ones in The Broken Sword are much more interesting. Yes, they are ugly and brutish, but they are also smarter, and while they have enough similarities to elves to produce offspring (with the help of magic), they are explicitly related to the Jotun of Norse myth.
Closing Thoughts
Anderson gives us some compelling stories. While not explicitly set in the same world, they are also not not the same world. His epic war of Good vs. Evil, Law vs. Chaos, is something that rings loudly even today in all editions of D&D. His wars of Christians vs. Pagans ring loudly to me.
His witches are less characters and more caricatures at times, but this fits into the world view these books have: the witches are just pawns and tools. Even when they have agency, their fate is already predetermined.
The entire time I was reading The Broken Sword, I could not help but wonder why witches didn't play a more prominent role in the game. Of course, the reason is simple. I was reading this looking for witches and not the larger themes. Gary, I assume, read these and saw the cosmic battle of Law vs. Chaos.
None of the witches in these two tales would make for good Player Characters. They would, however, make for great NPCs using the Dragon Magazine witch class.
In the AD&D Player's Handbook, it is mentioned that the Druid class is the same as the pre-Christian (not Gary's words) druid that has survived to Medieval times. If this is the case then certainly other "pagans" have survived. The witches of Poul Anderson certainly could be among those numbers.
