What 📔book(s) is the Rings of Power based on?

[Manwe]

I'm wondering since it also seems to have quite a few non-canon characters.

 

[Ugluk]

Not really anything that Tolkien wrote!

 

[Áramandë Amaniel]

As far as I know (and I might be wrong!), I believe they have no rights to The Silmarillion, HoME, LOTR or The Hobbit.

I think what they do have the rights to is the appendices at the end of LOTR (but I forgot which appendices).

Hence why they had to make up so many characters of their own that were not originally in Tolkien's works.

 

[Radaghast]

They do have the rights to The Lord of the Rings and The Hobbit, according to the showrunners. The show is very, very, VERY, loosely based on parts of the Appendices, but they have the rights to all of the Appendices.

 

[Rōmānus]

I'm wondering since it also seems to have quite a few non-canon characters.

I believe it is heavily based on the book Tolkien never wrote.