In Chapter 14 of The Wonderful Wizard of Oz, the King of the Winged Monkeys tells a story that comes off as a major tangent. It tells more about the history of the Winged Monkeys, but it also introduces seemingly important personages named Gayelette and Quelala who never again appear in the canon.
The King says, "There lived here then, away at the North, a beautiful princess, who was also a powerful sorceress. All her magic was used to help the people, and she was never known to hurt anyone who was good. Her name was Gayelette, and she lived in a handsome palace built from great blocks of ruby. Everyone loved her, but her greatest sorrow was that she could find no one to love in return, since all the men were much too stupid and ugly to mate with one so beautiful and wise."
There are a few interesting things to say about this, but let me first get out of the way that "mate" in this context doesn't refer to sex, although I suppose the sentence would still make sense if it did.
Anyway, Oz is divided into four countries, one for each of the main compass directions, but the North isn't visited or even named in Wizard. There are two hints that it exists, one being the presence of the Good Witch of the North and the other this story. The odd thing is that Gaylette's palace is made of ruby, yet the Gillikin Country's national color is revealed in the next book to be purple. While L. Frank Baum probably hadn't decided this at the time he wrote about Gayelette, why would the North and South BOTH use red?
Also, Gayelette comes across as a bit shallow. She does manage to find a husband eventually, however, by bringing up a handsome boy for the purpose, and using her magic to help him become handsome and wise. Shades of Pygmalion there, I suppose. You might think this would make Gayelette a lot older than her husband, but sorceresses in Baum's stories tend to have magic to keep themselves young. It isn't specifically stated that Gayelette does, but it would make sense.
On their wedding day, the Winged Monkeys throw Quelala in a lake, ruining his clothes. He takes it with good humor, but his bride does not, and initially wants to drown the Monkeys. Quelala intercedes for them, however, so instead she makes them slaves to the Golden Cap, a wedding present to Quelala that cost her half her kingdom. People in fairy tales are always spending half their kingdom on things, which I guess is how there get to be so many little kingdoms.
David Hulan's short story "The Gauds of Oz" attributes the making of the Cap to a jeweler named Joyero, who tires of ruling and trades back. He then trades the Cap to the Wicked Witch of the West in exchange for a rare jewel. The story is not canonical, of course, but it fits these things together nicely.
While the Monkey King reports that Gayelette was "beautiful and wise," he also portrays her as rather petty, perhaps appropriate considering who's talking. I mean, Gayelette DID enslave his tribe. It's certainly possible that the sorceress was good overall but had her flaws, presumably including being (in today's terminology) a bridezilla.
The more significant question here might be what happened to Gayelette. She was active in the time of Monkey King's grandfather, but we don't know how long Winged Monkeys typically live, and magicians tend to have long lifespans. So maybe she's still around, and some authors have utilized that possibility. She shows up in works by Roger Baum, Donald Abbott, and Marin Elizabeth Xiques.
Dennis Anfuso made her Glinda's mother, and Gili Bar-Hillel's "The Woozy's Tale" contains a brief reference to her being Glinda's cousin. I personally find the latter more likely, but who knows? I've also heard it suggested that Gayelette grew up to be the Good Witch of the North, which doesn't fit with what we're told about the Good Witch's past in Ruth Plumly Thompson's The Giant Horse of Oz.
March Laumer actually goes into quite a bit of detail about Gayelette's fate, with his Frogman revealing (SPOILERS) that Mombi turned her into a giant frog, and she eventually got together with the Frogman. Her marriage to Quelala wasn't quite the fairy tale romance it was made out to be, and I believe he ended up marrying a girl in Unnikegwick. As with most of Laumer's Oz writing, I find it to be a very clever solution, but I don't give it much credence in my own theories.