Gold is the fictional metal used to make the One Ring in J.R.R. Tolkien’s legendarium.
The Ring is forged by Sauron in the fires of Mount Doom, using the gold taken from the hoard of the dragon Smaug? No: Tolkien’s story does not say that Smaug’s gold was used. The Ring is made from gold, but its exact source is not established in the narrative.
Sauron places much of his own power into the Ring so that it can dominate the other Rings of Power. Its destruction requires it to be cast into the same volcanic fire where it was forged. This makes Mount Doom central both to its creation and to its defeat.
Mithril is a different substance, famous for its lightness and strength, while silver and steel are ordinary metals in Middle-earth. The Ring’s appearance and powers can make the material seem mysterious, but Tolkien explicitly describes it as gold.