Where to find information about the official DnD5e books title creatures?

I’m wondering where did the title characters from the official DnD5e books come from. What are their lores in the world of DnD 5e. I want to know more about: Tasha, Xanathar, Mordenkainen and Volo.

Where can I learn more about their stories? Is there any official information? Or are they only some cool naming for the books?

Is there any information about them in their books?