The Sunwell is a fount of ancient magical power located upon the Isle of Quel'Danas, within the High Elf Kingdom of Quel'Thalas. Created by Dath'remar Sunstrider using the vials of the former Well of Eternity, it empowered the newly born High Elf race for almost 7000 years until it was corrupted by the Death Knight Arthas Menethil, who used the power of the well to resurrect the necromancer Kel'thuzad transforming him into a powerful Lich and in turn cutting off the High Elves from their source of power. Fearful of the corruptive influence that the now tainted Sunwell would have on his people. Prince Kael'thas Sunstrider, son of Anasterian Sunstrider, ordered the Sunwell destroyed, which while preventing the corrupted energies from destroying what remained of his people, also gave them a withdrawal-based lethargy which would continue to plague the elven people for years to come.
The energy of the Sunwell, however, was not entirely snuffed out by the complete destruction of the well. Instead, the remainder of its energies manifested itself, with the help of the red dragon Korialstrasz, as a human woman known as Anveena Teague. Placed under protection by the elven people, now calling themselves Sin'dorei or 'Blood Elves' in honor of their fallen comrades, Anveena remained safe from harm until the events of the Outland Campaign, when Prince Kael'thas Sunstrider, now a corrupted servant of the Burning Legion, invaded Silvermoon and claimed Anveena and the Naaru known as M'uru before taking them both to the location of the Sunwell. There he prepared to summon forth his master Kil'jaeden but was stopped by the Shattered Sun Offensive, an order created by the merging of the Outland forces of the Scryers and the Aldor. Following the defeat of Kael'thas and his master Kil'jaeden the Draenei prophet Velen used the heart of M'uru, along with his own considerable power, to reignite the Sunwell as a source of powerful, pure energy once again.
Now that the Sunwell exists as a font of pure energy once more, the Blood Elf order of Paladins, known as the Blood Knights, have embraced the power of the well, forging a new identity for themselves far removed from the Order that once claimed the powers of the Light by force.
Creation of the Sunwell
The Sunwell was created as a fount of magical energy located on a convergence of ley energies. The well itself was created by Dath'remar Sunstrider who used a vial of water from the Well of Eternity which had been stolen from the Night Elves before their exile from Kalimdor. Once created, the energies from the Sunwell fed and strengthened all the High Elves in what would eventually become known as the Eastern Kingdoms. Deciding to create their new home in the land around the Sunwell, Dath'remar Sunstrider established Silvermoon City to the south of the Sunwell.
The Sunwell however, was not invulnerable to assault and as the High Elves grew in strength both physically and magically it became clear that protective measures were needed to keep the Sunwell safe from any threats. To do this the High Elven magi created several monolithic runestones on the borders of Quel'thalas. These runestones once completed, erected a powerful shielding magic which masked the presence of Quel'thalas from extra-dimensional invaders, as well as aiding in the protection of the land from any land or air based assault.
For several thousand years the Sunwell continued to supply the High Elven people with valuable magical energy. Generations passed and throughout all the generations, the High Elves cherished and protected the Sunwell and benefited from its power, even when they were far from the Sunwell itself.
The Third War: Destruction of the Sunwell
The Third War saw great loss visited on the High Elven people. An undead army known as the Scourge, which had claimed victory over the human kingdom of Lordaeron invaded the lands of Quel'thalas lead by Arthas Menethil. The once Prince of Lordaeron now Death Knight of the Scourge put the elven kingdom to the sword, his undead forces slaughtering the majority of the population. He killed the Ranger-General Sylvanas Windrunner and then laid siege to Silvermoon itself. Defending the great elven city was Belo'vir Salonar, Grand Magister of Quel'thalas and representative of House Salonar at the Convocation of Silvermoon. When the tide turned against the elves during the siege he ordered a fellow magister and close friend Rommath to evacuate as many civilians as possible and also teleport the surviving military to the Isle of Quel'Danas where they would make their final stand.
Soon after Arthas claimed the city of Silvermoon, but he could not yet reach the Sunwell with his army, as the shambling undead could not swim and he had no navy in which to cross the ocean to reach the island. To combat this, he used his formidable abilities granted to him as one of the damned and created an icy bridge which allowed his undead army to cross the ocean. Once on the Isle, his undead army once again clashed with the High Elves of Quel'thalas but despite the best attempts by the High Elven army, the Convocation of Silvermoon and King Anasterian Sunstrider, Arthas claimed his victory. In his wake, were thousands of dead elves. Anasterian Sunstrider, the Convocation of Silvermoon and Grand Magister Belo'vir were slain and there was no one to stop Arthas from his ultimate goal, to use the energies of the Sunwell to reanimate the remains of Kel'thuzad who would become one of the most powerful Liches in the known world as a result of the corruption that would befall the Sunwell.
With Arthas's goal reached, the former paladin turned death knight had no reason to remain within the ruins of the great kingdom. He and the bulk of his army departed, although many of the undead remained to hunt down any elves which had survived the massacre. The surviving elves, having no King to lead them or a Ranger-General to organize their military were scattered and lost. Taking temporary leadership, Lor'themar Theron, once the Ranger Generals second-in-command, rallied what survivors he could but it was not until the return of Prince Kael'thas Sunstrider, son of Anasterian Sunstrider, that the elven people had any renewed hope.
When Kael'thas returned, however, and in turn rallied his people, he realized that it was not the Scourge that was the true threat to his people at the time, but rather the corrupted Sunwell itself. The dark energies that now radiated from the once pure source of energy were slowly corrupting the elven people and Kael'thas knew that unless something was done, all High Elves would be eventually killed by this corruptive influence. Faced with no other option, Kael'thas, his most loyal magi and what volunteer soldiers he could muster returned to the Sunwell and once there, they destroyed the Sunwell entirely.
Sadly while Kael'thas recognized that it was the only way to save his people, he could not have predicted events that would have happened after its destruction. While some of the energy of the Sunwell was preserved, due to the machinations of the red dragon Korialistrasz and would come into play in future events, the most crippling side effect was the withdrawal effect. The elven people had grown so accustomed to the energies of the Sunwell that now, with the energies gone, they began to suffer withdrawal symptoms. Many elves, especially the young and the old fell ill and a large number of the survivors, who had narrowly escaped death at the hands of the undead, succumbed to the effects of their withdrawal either dying outright or becoming twisted and wretched versions of their former selves, craving above all else the magical energy that they had become addicted to.
The elven people never forgot the lives that had been claimed by the Scourge however, and in order to honor those that had given their lives in the defense of their once great nation the High Elves, or Quel'dorei as they were known in the elven tongue, changed their name to Sin'dorei or Blood Elves. From that point on they were the Children of the Blood, forever honoring their fallen comrades in every moment of their lives.
In the aftermath of the Third War, some months after the destruction of Silvermoon the Scourge once again reared its ugly head in an attempt to snuff out the elven people. Lead by Dar'Khan Drathir, a former magister of Silvermoon turned traitor and agent of the Scourge, the undead forces clashed with the elves in Quel'thalas once more. Dar'Khan battled with Anveena Teague, the Avatar of the Sunwell who had been created by Korialistrasz some months earlier. Along with a small band of heroes and the blue dragon Kalecgos, the armies clashed and Dar'khan was defeated. Following the battle Anveena and Kalecgos remained within Quel'thalas, shielded by powerful magic so that they may restore the land to its former glory. Anveena's true identity as the Avatar of the Sunwell would remain a closely guarded secret, with only a few people knowing the truth including both Lor'themar Theron and Prince Kael'thas Sunstrider. While no one saves for the venerable bronze dragon Nozdormu could have known, it was a critical mistake to have given Prince Kael'thas that knowledge, but for the time being Anveena was safe, and it would be many years before events would once again turn against the elven people.
The Shattered Sun Offensive
The Shattered Sun Offensive was yet another chaotic period for the elven people. The Blood Elves had broken their ties to the Alliance years earlier and with the aid of the Forsaken, who were lead by the elves former Ranger General, Sylvanas Windrunner the Blood Elves had managed to join the Horde and consolidate much of their power, although they were still very much shadows of their former selves.
Prince Kael'thas by this time had been in the distant land of Draenor, also known as Outland, and when the Dark Portal once again opened allowing access to the former homeworld of the Orcs the Blood Elves rushed through the portal, eager to reunite with their Prince. What they discovered, however, was something far worse than they initially believed possible. Prince Kael'thas Sunstrider had betrayed the Elven people by throwing his power behind none other than the Burning Legion, who were the true architects of the undead forces that had ravaged their homeland so many years ago. He and his forces were defeated at Tempest Keep, but through the use of demonic magic by a Shivan Priestess, Kael'thas was fully corrupted and with an army of his own Felblood tainted elves he invaded Silvermoon, capturing the Avatar of the Sunwell and the Naaru, M'uru, whom the elves had been using as a siphon to gain control over the light and form their own branch of paladins. His forces claimed the Isle of Quel'Danas and the Sunwell itself, which Kael'thas intended to use as a doorway to allow his master, Kil'jaeden the Deceiver into the world of Azeroth.
To combat this threat a coalition was formed. This force was compromised of two orders that had at one time been the bitterest of enemies. The Scryers, a group of Blood Elves who at one time had served Kael'thas but had turned against him and joined with the Naaru, A'dal and the Aldor, a group of Draenei who could not forgive the Scryers for the lives they had taken in the name of Kael'thas before their defection. Both of these factions however united under a single banner, their military forces combining into the Shattered Sun Offensive and supplemented with the aid of both the Alliance and the Horde, they pushed into the Isle of Quel'Danas and took the fight to Kael'thas and his master Kil'jaeden.
The resulting campaign was a great success. Kael'thas was slain within the Magister's Terrace and within the depths of the Sunwell many demons and Felblood elves were slain before Kil'jaeden himself was cast back into the twisting nether. Following the defeat of the demon lord, the forces of the Shattered Sun assembled within the Sunwell chamber. There, Lady Liadrin of the Blood Knights watched on as Velen, the Prophet leader of the Draenei people used the pure heart of the fallen Naaru, M'uru to reignite the Sunwell, turning it once more into a fount of pure energy. The Sunwell is now a combination of both Arcane and Holy energies, owing to the heart of the Naaru used to restart it. While different to the Sunwell's energies of old, it remains an inexhaustible source of power capable of feeding the Thalassian people no matter where they are on Azeroth.
During preparations for the battle on the Broken Shore, a group of blood elf paladins use the power of the Sunwell to enchant their Horde allies' weapons with holy might. The priests of Netherlight Temple later retrieve a fragment of Light from the Sunwell, among other holy places on Azeroth.
The Sunwell is visited by Lor'themar Theron, Grand Magister Rommath, Lady Liadrin, First Arcanist Thalyssra, Arcanist Valtrois, Silgryn, and Alleria Windrunner. The visit was intended as a gesture of goodwill for the Nightborne leaders and a courtesy for Alleria; while the latter was estranged from Silvermoon's political climate, Lor'themar would not deny a daughter of Quel'Thalas' request to see their people's most sacred site. Alleria's presence attracts a group of void creatures, who spill into the plateau at Nether-Prince Durzaan's command and begin spreading their corruption. The heroes, along with the Sunwell's magi, wardens, and spellbreakers, sortied to battle the void beasts and prevent the Sunwell's corruption. A powerful void horror, Aruun the Darkener, then emerged in an attempt to contaminate the well directly but was stopped and killed. Finally, a rift portal was opened directly above the Sunwell's waters, but Rommath, Thalyssra, and Alleria combined their magic to close it before catastrophe struck. In the aftermath of the battle, Alleria was exiled by Lor'themar, on the grounds that her very presence poses a threat to Quel'Thalas and the Sunwell. The battle's outcome also endeared the regent to Thalyssra, who pledged her kingdom to the Horde.
Rommath had previously demanded Magister Umbric's group be exiled for similar reasons, as those who treat with the void are a danger to the Sunwell.
Adapted from WoWPedia