Fëanor improves the written alphabet of Rúmil
Event Type: Cultural/Social
Age: Time of the Trees
In this time  began the flowering of the skill of Fëanor son of Finwë, who was of all the Noldor the greatest maker and craftsman. And he took thought and devised new letters, bettering the devices of Rúmil, and those letters the Eldar have used ever since that day.
Morgoth's Ring, HoME Vol 10, Part 2, The Annals of Aman
In his youth..., [Fëanor] devised those letters which bear his name....
The Silmarillion, Quenta Silmarillion, Ch 6, Of Fëanor and the Unchaining of Melkor
The Tengwar were... ancient; for they had been developed by the Noldor, the kindred of the Eldar most skilled in such matters, long before their exile. The oldest Eldarin letters, the Tengwar of Rúmil, were not used in Middle-earth. The later letters, the Tengwar of Fëanor, were largely a new invention, though they owed something to the letters of Rúmil. They were brought to Middle-earth by the exiled Noldor, and so became known to the Edain and Númenóreans. In the Third Age their use had spread over much the same area as that in which the Common Speech was known.
The Return of the King, LoTR Appendix E, Writing and Spelling: Writing
Elena Tiriel 14Mar08