The dragon defeated by Túrin Turambar in Tolkien’s legendarium is Glaurung.
Glaurung is known as the Father of Dragons and appears in the stories of the First Age. He serves Morgoth and uses both fire and powerful speech to bring ruin to the people of Beleriand. In the tale later published as The Children of Húrin, Glaurung manipulates Túrin and his sister Nienor while contributing to the destruction of the kingdom of Nargothrond.
Túrin eventually confronts the dragon at Cabed-en-Aras. He kills Glaurung by stabbing him from below with his sword Gurthang, but the victory does not undo the dragon’s earlier deception or the tragedy that follows. Glaurung’s death is therefore a major event in Túrin’s story, not a simple heroic triumph.
Glaurung is distinct from Smaug, the dragon in The Hobbit, and from Ancalagon the Black, the enormous dragon who fought in the War of Wrath. Tolkien’s dragons belong to different ages and stories, so identifying the specific tale is essential.