Gringott's Dragon

"A gigantic dragon was tethered to the ground in front of them, barring access to four or five of the deepest vaults in the place. The beast's scales had turned pale and flaky during its long incarceration under the ground; its eyes were milkily pink; both rear legs bore heavy cuffs from which chains led to enromous pegs driven deep into the rocky floor. Its great spiked wings, folded close to its body, would have filled the chamber if it spread them, and when it turned its ugly head toward them, it roared with a noise that made the rock tremble, opened its mouth, and spat a jet of fire that sent them running back up the passageway."

- Description of the dragon in 1998.

This dragon (more specifically part of the Ukrainian Ironbelly species) was used to guard several high-security vaults, including the Lestrange Vault, at Gringotts Wizarding Bank. It was encountered by Harry Potter and his friends when they infiltrated the bank in 1998, although it is likely the dragon had been guarding the vaults for a long time prior to this.

Early History
It is unknown when exactly this particular dragon was placed to guard the vaults it was assigned, but it is known that during this time it was trained to fear the sound of the Clankers as it expected pain upon hearing it, causing it to retreat and allow those with using the Clankers to access the vaults. This was most likely achieved using the process of classical conditioning. The dragon was aged and half-blind by the spring of 1998.

1998 Break-In of Gringotts
As Harry Potter, Ron Weasley, and Hermione had been planning to break into the Lestrange Vault for a few weeks ahead of time, they fully expected to find the dragon and were able to use the Clankers (with the help of Imperiused goblin Bogrod) to drive it away and get into the vault.

"Nevertheless, as they climbed higher and higher, London unfurling below them like a grey-and-green map, Harry's overwhelming feeling was of gratitude for an escape that had seemed impossible. Crouching low over the beast's neck, he clung tight to the metallic scales, and the cool breeze was soothing on his burned and blistered skin, the dragon's wings beating the air like the sails of a windmill."

- Harry Potter, Ron Weasley, and Hermione Granger escape on the dragon. After the goblin Griphook abandoned them and they were carried out of the vault in a cascade of treasure, Harry, Ron, and Hermione jumped onto the back of this dragon in desperation to avoid the charging wizards and goblins. Hermione severed the dragon's chains and used a Gouging Spell to help the dragon carve its way out of the tunnel and toward the surface. The other three pitched in, and the dragon crashed through the Gringotts hall, out into Diagon Alley, and took off. They soared on the back of the dragon for a while, but finally jumped off into a lake as the dragon lowered it's flying height nearer to the water's surface. Although Hermione expressed concern for leaving the dragon in the wild, Ron was confident it would be able to defend for itself without difficulty.

Physical appearance
The dragon was a large, savage creature with enormous spiked wings and an ugly head with partially blind eyes a milkily pink colour. Due to being underground for so long, the dragon's scales were pale and flaky, and it bore the marks of its brutal treatment from goblins: scars on its face made by vicious slashses across its face from, Harry guessed, hot swords. Prior to its escape, both of its rear legs had heavy cuffs on them with chains leading to massive pegs driven far into the rocky floor of the subterranean chamber. The dragon's roar was said to make the rock tremble, and it was known to breathe jets of flame.

Behind the scenes

 * This dragon's species was not identified in the novel. It was stated to be a Ukrainian Ironbelly in Harry Potter and the Deathly Hallows: Part 2.
 * In 1991, when Rubeus Hagrid talked to Harry about Gringotts (the first time), he told him rumours about there being dragons guarding Gringotts vaults. Harry, taking interest, tried to coax Hagrid to tell him more about the dragons. Harry also sees a flash of flame and leans out of the cart to investigate, but is hastily pulled back in by Hagrid. However, he does not seem to take any interest in the rest until its appearance in 1998.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 2

Dragon de Gringotts