The Dwarf who helped build the Doors of Durin was Narvi. He was a renowned craftsman of Khazad-dûm, the Dwarven kingdom better known by its later name, Moria.
Narvi collaborated with Celebrimbor, the Elven-smith and lord of Eregion, during the Second Age. Narvi constructed the western gate itself, while Celebrimbor created the decorative ithildin designs and inscriptions. The partnership reflects the unusually close friendship and trade relationship between the Dwarves of Khazad-dûm and the Elves of Eregion.
The inscription on the doors preserves Narvi’s role: it identifies him as the maker and Celebrimbor as the designer of the signs. The lettering is in Sindarin written with Tengwar, allowing Gandalf to translate the famous instruction, “Speak, friend, and enter.”
Narvi is easy to confuse with Durin, who founded Moria and gave the gates their name, or with Gimli and Thorin, who are important Dwarves from later stories. Neither Gimli nor Thorin was involved in constructing the Doors of Durin. Narvi’s work dates from long before the events of The Hobbit and The Lord of the Rings.