Fëanor created the Tengwar writing system used for many Elvish inscriptions. In Tolkien’s fictional history, the Ñoldorin Elf invented it in Valinor after earlier work by Rúmil had produced the Sarati script.
The Tengwar were first used for Elven languages including Quenya and Telerin. They later spread to other languages, especially Sindarin, and Tolkien also used the script for examples of English. Its letters are designed around the sounds they represent: related shapes often indicate related places or manners of articulation.
The word tengwar is the plural of tengwa, meaning a letter or sign. Different “modes” adapt the same basic system to different languages. In the mode of Beleriand, for example, vowels and consonants are written as full letters, while other modes use vowel marks called tehtar.
A famous complication is the One Ring inscription. It is written in Tengwar letter-forms but records Sauron’s Black Speech, not an Elvish language. Pengolodh, Celebrimbor, and Daeron are associated with other lore, but they did not create the Tengwar.