In J.R.R. Tolkien’s mythology, the first dragon is Glaurung.
Glaurung appears in the stories of the First Age and is described as the first of the great dragons bred by Morgoth. He is initially wingless, unlike the later winged dragons, and serves Morgoth during the wars against the Elves and Men of Beleriand. His emergence from Angband marks an important escalation in Morgoth’s military power.
Glaurung is central to the tragic story of Túrin Turambar. He uses his intelligence and hypnotic power to manipulate Túrin’s sister, Niënor, and contributes directly to the destruction of their family. Tolkien developed this material in several forms, including The Children of Húrin and earlier versions of the legendarium.
Glaurung is not the same dragon as Smaug, who belongs to The Hobbit and the Third Age. Ancalagon the Black is another First Age dragon and is described as the greatest of the winged dragons, while Scatha belongs to a later period.