I'm wondering where the characters in the titles of official D&D 5e books came from. What is the lore behind Tasha, Xanathar, Mordenkainen and Volo?
Where can I learn more about their stories? Is there any official information or are they only cool names for the books?
Is there any information about them in their books?
There is some information in their respective books, but it's not much, I'm afraid.
Introduction in Tasha's Cauldron to Everything:
Tasha's Cauldron of Everything offers a host of new options for DUNGEONS & DRAGONS, and our journey through those options is accompanied by the notes of the wizard Tasha. Creator of the spell Tasha's hideous laughter, Tasha's life is one of the most storied in the D&D multiverse. Raised by Baba Yaga, the Mother of Witches herself, Tasha adventured across the world of Greyhawk and became the friend and sometimes enemy of other famous adventurers, like Mordenkainen. In time, she ruled as the Witch Queen and later changed her name to Iggwilv - a figure of legend who is whispered about, feared, and admired.
There are also notes from Tasha spread among the book, from which we learn that her aliases are Natasha the Dark, Hura of Ket, Baba Yaga's Daughter or witch by excellence, and that she loves insects, for example.
Introduction in Xanathar's Guide To Everything
Beneath the bustling city of Waterdeep, a beholder crime lord keeps tabs on everyone and everything—or so the beholder thinks. Known as Xanathar, this bizarre being believes it can gather information on everything in the DUNGEONS & DRAGONS multiverse. The beholder desires to know it all! But no matter what the beholder learns and what treasures it acquires, its most prized possession in all the multiverse remains its goldfish, Sylgar.
Again, we can learn some things from his notes throughout the book, like he's glad to live underground because there is no weather, or that he's not sure whether he likes music or not.
No short introduction here, but we can learn some things from the notes at the beginning of the book:
Mordenkainen is an Oeridian wizard from the world of Greyhawk who travelled the multiverse with his apprentice Bigby to observe conflicts of all sorts.
Sprinkled throughout the book are observations and musings from two denizens of the Forgotten Realms: the legendary explorer Volothamp Geddarm (Volo to his friends) and the Archmage of Shadowdale himself, Elminster Aumar.
Here again, some notes throughout the book give hints about the personality of Volo.
Iggwilv (aka Tasha) is a fictional wizard from the Greyhawk campaign setting for the Dungeons & Dragons roleplaying game. She was created by Gary Gygax.
She dates back to 1st edition.
The crime lord of Waterdeep was introduced with the Forgotten Realms boxed set.
Was Gary Gygax’s PC.
Dates back to 2nd edition with his range of “Volo’s Guide to” every piece of FR crap people would buy.
On top of some information in their respective books some characters are also a part of waterdeep: dragon heist.
Volo is the introduction to Waterdeep: dragon heist and gives the players their first quest. He also talks about a new book he's writing. Waterdeep dragon heist also features an introduction to Waterdeep written by Volo himself which also includes some insights to his character.
Xanathar is a possible villain of Waterdeep dragon heist and as such has his character described in the book. The book also includes a number of his goons and insights on his gang.
Another source I can think of is Baldur's Gate 3. The game came out not too long ago in early access and features Volo as an NPC and gives a good overview of his character.
Finally the forgotten realms wiki is always a good source to procure some information and has more sources linked. On top of that it also has a list of appearances for some of the characters.
Assuming that those lists are correct Mordenkainen has some appearances in Curse of Strahd and Baldurs Gate: Descent into avernus, while Volo also appears in Tomb of Annihilation and Waterdeep: Dungeon of the mad mage as well as a number of novels and other games.
