Though Glaurung was named Father of Dragons, the greatest Dragon that ever entered the world was Ancalagon The Black. He is said to have extremely hot fire. In The Fellowship of the Ring, Gandalf says to Frodo, "It has been said that dragon-fire could melt and consume the Rings of Power, but there is not now any dragon left on earth in which the old fire is hot enough; nor was there ever any dragon, not even Ancalagon the Black,who could have harmed the One Ring, the Ruling Ring, for that was made by Sauron instead." This shows that Ancalagon had particularly powerful fire. Rushing Jaws is the meaning of his name, and his ravening majesty halted the Host of Valinor in the War of Wrath at the end of the First Age of the Sun. Ancalagon was the first of the winged Fire-Drakes, and he and others of that breed came out of Angband like a mighty storm-cloud of wind and fire as a last defense of Melkor's realm.
This was the first the world had seen of winged Dragons and for a time Melkor's armies were advancing. Yet the flying Vingilot and the warrior Eärendil came out of the west. The battle of these beings lasted for a long while, but in the end, Eärendil was victorious. Ancalagon the Black was cast down and the other Dragons fled or were slain. So the War of Wrath ended and Melkor's power was broken, and Ancalagon's death marked the decline of Dragons.
Ancalagon was huge beyond imagining, his wings able to blot out the light of the sun even from afar, and large enough to severely crack the volcanic Thangorodrim, the tallest peak in Middle-Earth.
How a monster so huge was killed has not been stated. However, the Silmaril likely played a part, as with the Eagles. Eärendil might have tried to rip the dragon's wings, letting him crash onto the sharp peaks below.