Eärendil, accompanied by the Eagles of Manwë, came out of the west in his ship Vingilot; they fought Ancalagon and the other dragons, and eventually came out victorious. Eärendil cast Ancalagon upon the triple-peaked towers of Thangorodrim, destroying both the towers as well as the dragon. The fall of Ancalagon marked the end of Morgoth's final resistance.
Ancalagon was so large that his wings were able to block out the light of the sun from afar; his body was strong enough to destroy the towers of Thangorodrim, the highest peaks in Beleriand. And like other Urulóki, he breathed fire which was said to be hotter than any other known flame.
However, Gandalf notes that while his powers were great and the heat of his fire unmatched by any other dragon, Ancalagon's fire was not powerful enough to destroy the One Ring:
"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 himself." (Fellowship of the Ring)
Sindarin "rushing jaws" - from anc ('jaw') + alag ('impetuous')