Nolaloth

Nolalothcaragascint (or simply Nolaloth) was an ancient dragon that was asked by the Illefarn Empire to destroy their great Guardian following the fall of Netheril.

Nolaloth v. King of Shadows
The Guardian had been created from one of Illefarn's greatest champions, his soul tied to the ancient Weave to become a construct of power great enough to deter Netherese attack. But when the Netherese arcanist Karsus, fearing the empire's destruction by the life-draining phaerimms, cast the 12th level spell Karsus's avatar, and then-goddess of magic Mystryl sacrificed herself to save the Weave, the Weave ceased to exist long enough for the Guardian to lose its power source. Instead of accepting its fate and dying, however, it linked itself to Shar's Shadow Weave and became the King of Shadows.

Following the King's defeat of several mighty Illefarn warriors, the ruling council of Illefarn asked the great wyrm Nolalothcaragascint to destroy it in exchange for a massive addition to his hoard from the empire's coffers. The dragon accepted, and flew into battle. A titanic struggle erupted that shook the Sword Coast, but in the end the King of Shadows overcame the dragon and struck him to the earth, creating a massive valley in the Sword Mountains which remains to this day. The dying Nolaloth was "saved" by the ruling council, which transfigured his heart into an enormous floating crystal, into which the wyrm's soul was laid in a process reminiscent of the crafting of a lich's phylactery.

Thankfully for Illefarn, the dragon's sacrifice was not entirely in vain: the King of Shadows was so badly injured in the battle that it was forced to retreat to the Plane of Shadow to recover, where it remained for over a thousand years.

Advisor to heroes
Over the centuries, the great wyrm's valley became an oasis of fertility in the Sword Mountains, warm year-round thanks to the heart's influence, and a haven for young dragons of all species. Though immobile, the great drake could still speak, and people occasionally came to him to learn, particularly about the King of Shadows.

First to come were the githyanki. Approximately a thousand years before the events of Neverwinter Nights 2, the King of Shadows made its first forays into the universe outside the Shadow Plane. It forced open a portal into the Astral Plane, sending its Nightwalker avatar to attempt conquest in the name of now-defunct Illefarn. The giths' silver swords were enough to fight it off, but at a terrible cost in lives, and the King simply shrugged and recreated the Nightwalker. The Lich-Queen Vlaakith sent her warriors to Faerûn to learn more of her people's seemingly indestructible foe, and found Nolaloth in his valley. He advised them to attack the portal itself, extracting a return promise that the githyanki would return him to life. The githyanki were successful, but either forgot or ignored their promise.

In the mid- to late-1200s DR, then-Neverwintan jester mage Ammon Jerro, while studying in his time off, uncovered information leading to the King of Shadows, information that explained some recent strange happenings on the Sword Coast North. His search for answers eventually led him to Nolaloth, and in exchange for the same promise he extracted from Vlaakith's emissaries (to return him to life), the dragon informed him of the githyanki's success against the King with their silver swords, and told him of the mightiest silver sword of them all: the Silver Sword of Gith, lost with its wielder millennia ago in the Nine Hells. Only the Sword of Gith might have the power to unmake the King once and for all.

Jerro immediately left for the Nine Hells, recovered the Sword with the aid of Levistus, Lord of the Seventh Circle, and then led a force of Neverwintan soldiers into battle against the King of Shadows in the Mere of Dead Men. The King was once again defeated, but the Sword was shattered (one shard burying itself in the chest of the infant Kalach-Cha), and Ammon Jerro was blown into the Hells.

Encounter with the Kalach-Cha
In either late 1373 DR or early 1374 DR (the canon is not clear on this point), the Kalach-Cha, now Knight-Captain of Crossroad Keep, was informed by her githzerai ally Zhjaeve that she needed the Silver Sword of Gith to defeat the now-thrice-resurgent King of Shadows. Ammon Jerro, having escaped from the Hells and now working with the Kalach-Cha, told her of how he had learned from Nolaloth. The party immediately left for the dragon's valley.

As they stood below the great crystal heart, they noticed a pair of black dragons perched on the cliffs above, simply watching them. They proceeded warily into the northern passage, where they encountered Nolaloth himself. At first Nolaloth refused to help them, his ghostly head vanishing, but then the Kalach-Cha mentioned the return of the King of Shadows. Nolaloth agreed to help them, telling that to reforge the Sword of Gith, they must return to where it was broken: a scar on the earth in West Harbor. This time, the dragon was tired of living half a life, and asked the Kalach-Cha to repay him for his aid by destroying his heart, and freeing him from his torment.