J.R.R. Tolkien used Tengwar for the inscription on the One Ring.
Tengwar is a writing system created by Tolkien for the languages of his fictional world. In the story, the Ring inscription is written in Tengwar characters, although the words themselves are in the Black Speech of Mordor. The inscription begins, “Ash nazg durbatulûk,” and describes the power of the One Ring over the other Rings of Power.
This distinction between script and language is important. Tengwar is the writing system, while the Black Speech is the language being represented in the inscription. Readers sometimes call the inscription “Elvish” because Tengwar is strongly associated with the Elves, but its particular text is not written in an Elvish language.
Tolkien designed several scripts, including Cirth, a runic system used by different peoples in Middle-earth. Tengwar remains his most widely recognized invented script and appears throughout maps, illustrations, and adaptations.