Though Glaurung was named Father of Dragons, Ancalagon also known as Ancalagon The Black was one of the most powerful and infamous of all the dragons bred by Morgoth during the first First Age and possibly the largest dragon to have ever lived. His fire was hotter than most other dragons.
Ancalagon's size is not specified, but may be gigantic due to the destruction of "the towers of Thangorodrim", which are elsewhere identified with the three smoking peaks of the mountain. He was however, said to be as big as a mountain. However, his size is never directly specified and some powerful but small creatures are able to cause great destruction even in death, such as Durin's Bane breaking the slopes of Celebdil. Like all other Urulóki, Ancalagon breathed fire, which was said to be hotter than any other dragon's flame.
Powers and Stats
Tier: 6-B via powerscaling
Name: Ancalagon the Black
Origin: Lord of the Rings
Classification: Original Winged Dragon
Speed: Supersonic+ to High Hypersonic flight speed via power-scaling
Lifting Strength: Unknown
Striking Strength: Country Class
Durability: Country level
Range: Hundreds of kilometers due to his size alone (So large he can blot out the sun even from ridiculously high up)
Standard Equipment: N/A
Weaknesses: Nothing notable (How he died was not confirmed but he was in battle with Earendil and the Eagles)
Note: Ancalagon's history and powers were not explained much in the Silmarillion: Ancalagon the Black