The One Ring bears the Black Speech inscription beginning “Ash nazg durbatulûk.”
The inscription is a shortened form of the Ring-verse: “One Ring to rule them all, One Ring to find them, One Ring to bring them all and in the darkness bind them.” The writing appears only when the Ring is heated, revealing fiery letters in the language of Mordor.
Sauron forged the One Ring in the fires of Mount Doom during the Second Age. He designed it to dominate the other Rings of Power, but its destruction became the central objective of The Lord of the Rings. Frodo carries it to Mordor, and the Ring is finally destroyed in the Cracks of Doom.
The Ring of Barahir, Narya, and the Silmarils are important objects but are not inscribed with this verse. The language is the Black Speech, while the object carrying it is the One Ring.