Kilgharrah

The Great Dragon is a mighty dragon who was imprisoned and chained in a cave beneath Camelot by Uther Pendragon at the conclusion of The Great Purge. He served as a mentor to Merlin, telling the boy of his destiny to protect Prince Arthur Pendragon and help him become king of Albion (The Dragon's Call; The Mark of Nimueh).

The Dragon gives Merlin advise on how to solve challenging problems and even directly helps him at times. However, Merlin did not always do as the Dragon advised. For example, Merlin decided to save the druid boy Mordred despite the Dragon saying he would eventually kill Arthur (The Beginning of the End). He also decided to help save Uther when he overheard Morgana conspiring to kill him, despite the Dragon's advice to let him be killed (To Kill the King).

The Dragon appears to possess foresight, evidenced by his claims regarding Arthur's destiny, and his prophecies concerning Mordred's role in Arthur's future (The Beginning of the End). When Arthur's dead uncle was resurrected as a wraith, the Dragon aided in the creation of a sword capable of destroying Tristan (Excalibur).

Merlin and the Dragon had a major falling out during the time when Arthur was dying from a Questing Beast's bite. In order to save Arthur's life, Merlin was told by the Dragon that he had to go the the Isle of the Blessed and accept the price. Merlin found out the price was another person would have to die in Arthur's place. Merlin agreed to sacrifice his own life, but Nimueh, an Old Religion high priestess, took his mother instead. Merlin went to the Dragon and accused him of tricking him. The Dragon agreed with this, telling him it is Merlin's destiny to protect Arthur until he claims his throne, at which time the Old Religion will be allowed to resurface and he would be free. Realising that was all the Dragon ever cared about, Merlin swore he would never allow him to be free. Angered, the Dragon tried to kill him. Merlin conjured a shield and escaped. The discord appears to have increased due to Merlin's killing of Nimueh (Le Morte d'Arthur).

Despite Merlin's vow to never return to him, Merlin does return for the Dragon's advice and is forced to promise to free the dragon some day, for the knowledge of how to defeat Cornelius Sigan who has conquered mortaility (The Curse of Cornelius Sigan).

Merlin sought the Dragon again when Morgana's magic began to reveal itself and she became terrified. Merlin wanted to know where the Druids were so Morgana could seek their help. But the Dragon said it would be best if Morgana, who he confirmed was a witch, never knew the full extent of her powers, and refused to aid Merlin if he was planning to aid her. Despite the Dragon reminding Merlin of the consequences of his ignoring his advice in the past, Merlin defiantly chose to help Morgana (The Nightmare Begins).

Merlin later returned to the Dragon after Uther had been enchanted into marrying a troll, a happening that the Dragon found very funny. The Dragon gave Merlin the knowledge on how to break the troll's spell, and also reminded Merlin of the deal he had made with him (Beauty and the Beast: Part Two).

Later, Merlin used magic for his amusement and a villager witnessed it, though she didn't know he had done it. She reported it to Uther, who sent for the dreaded witchfinder Aredian. Aredian, after searching for any sign of magic, pubically accused Merlin of being a sorcerer, but Gaius took the blame. Merlin went to the Dragon for advice on how to help Gaius. At first, the Dragon rebuked him for wanting to reveal himself, saying Aredian would simply kill him along with Gaius. When he saw how distressed Merlin was, the Dragon, in honest regret, infromed Merlin that he couldn't help him because he didn't know how to. Merlin later exposed Aredian's treachery and framed him for sorcery, which resulted in the witchfinder's death and Gaius' freedom (The Witchfinder).

The Dragon later advised Merlin when Arthur was enchanted into loving a princess, saying that only the one Arthur truly loves could break the enchantment (Sweet Dreams).

During Merlin's next visit, the Dragon asked him to uphold his promise and set him free. Merlin said he would, but only when he knew Camelot was safe. Merlin asked the Dragon about a crystal that Morgana had stolen. The Dragon said the crystal only works for those who can use its power, but for those who can it can tell the future. He then told Merlin why he had warned him about Mordred and Morgana: prophecy speaks of an evil alliance between them. Sometime later, Merlin got his hands on the crystal and saw a future where the Dragon attacked Camelot once he was free. This has clearly shaken Merlin, and he is now torn between upholding his promise and protecting Camelot. (The Witch's Quickening)

Merlin, despite his vision of the future, later fulfilled his oath to the Dragon and used a sword stolen from one of the Knights of Medhir to free him. This, however, would have dire consequences for Camelot: the Dragon, full of rage, attacked the kingdom. Merlin was later forced to find the last Dragonlord so the Great Dragon could be defeated before he destroyed Camelot. Merlin found Balinor, who was also his father. Balinor said the powers of dragonlords were passed on genetically, and therefore Merlin had the power to command the Dragon. Merlin managed to stop the Dragon, but showed mercy by banishing him from Camelot forever. The Dragon, before departing, told Merlin he was sure their paths would cross again.

Personality
The Great Dragon acted as a mentor to Merlin and was very wise though he tended to speak in riddles which sometimes irritated Merlin. The Dragon appeared to be able to see into the future though it's also possible he learnt of Merlin's destiny from someone else who could see into the future. Either way the Dragon possessed great knowledge of the future and Merlin found his advice useful though he didn't always follow it. A notable example of this was when the Dragon made a prophecy about Mordred killing Arthur but Merlin rescued Mordred despite this prophecy.

During the last episode of season 1 the Great Dragon revealed that he was only helping Merlin in order to gain his freedom. When Merlin told him that he would never be freed the Dragon was enraged and even tried to attack Merlin with fire but Merlin blocked it with a magical forcefield. In season 2 however Merlin was forced to come back and visit the Dragon in order to stop Cornelius Sigan who had apparently conquered mortality. The Dragon made Merlin promise to free him and Merlin reluctantly agreed. When he was finally freed however the Dragon attacked Camelot in order to take revenge both for the extinction of his kind and for his long imprisonment. Merlin, having inherited the powers of the Dragonlords from his father, Balinor, forced the Dragon to leave Camelot but before he left the Dragon told Merlin that he believed their paths would cross again.

Although the Dragon acted mostly for selfish reasons, he was capable of thinking of others and felt genuinely sorry for Merlin when he told him he would be unable to help him save Giaus (The Witchfinder). In season 1 Merlin considered the Dragon a friend but became a lot less trusting after the Dragon revealed he was acting to gain his freedom.

The Dragon also possessed a slightly strange sense of humour and usually displayed this humour at inappropriate times. For example when Merlin told him that Uther Pendragon's new wife was a troll the Dragon went into a fit of laughter while Merlin couldn't see the funny side of it. He also laughed about Morgana when Merlin told him that she had stolen an important crystal. Despite Merlin's protests the Dragon often called Morgana a witch.